Abstract: Blind guide device is disclosed. The device comprises a light-emitting element, a first electric circuit for generating an electric pulse and causing pulsating-conduction of the light-emitting element, a first lens for converging the light emitted from the light-emitting element onto a body to be detected, a mark attached to the body to be detected for performing retroreflection action, a second lens and a photo-detector element for receiving the light reflected by the body to be detected and the mark, a second electric circuit for amplifying the output electric signal of the photo-detector element and holding an electric signal synchronized with the electric pulse, a third electric circuit for generating an electric signal whose frequency or amplitude varies in response to the output electric signal of the second electric circuit, and an electro-acoustic transducer or vibrator for converting the output electric signal of the third electric circuit into a sound or into a stimulation.

Abstract: A device for monitoring environmental exposure includes an element whose electrical properties change, in a predetermined way, in response to the environmental exposure. The element may be part of a tuned circuit or of a shield for a tuned circuit. In either case, when the tuned circuit is interrogated, preferably by an r.f. or microwave signal, it emits a signal whose intensity depends on the electrical properties of the element. Thus, an incremental environmental exposure can be measured by a change in the signal intensity. The device is particularly useful for monitoring the condition of perishable materials, because it can be located with the perishable inside a packaging material during both storage and interrogation.

Abstract: The invention is concerned with a device for the detection of moving objects which are warmer or cooler than a static environment. The device consists of a detector unit (1) connected to a preamplifier (2), a signal processing unit (3), and output detector device (4). The device is characterized in that the detector unit consists of a conventional Peltier element (5), one of whose sides (6) is placed in good thermal contact with a heat sink (8) and that the other side (7) of the Peltier element (5) is used as a radiation-sensitive detector surface. This radiation-detecting surface may be provided with a radiation-absorbing layer (9). The current supply terminals (10, 12) of the Peltier element are connected to a band-pass filter (11) which, in turn, is connected to a low-noise preamplifier (2). By having the electronic circuitry based on C/MOS technology, and since the detector draws no current, provision of a suitable battery makes the unit self-sufficient for approximately ten years.

Abstract: A passive safety probe for placement in a time varying magnetic field to alert personnel when the power density of high intensity electromagnetic fields reach and exceed applicable personnel safety limits. The probe senses the magnetic field present with a loop antenna. The loop antenna produces a voltage output in response to the magnetic field. The output voltage is linearized by a frequency dependent filter and rectified to provide a direct current output which is subsequently coupled to an attention getting indicating means such as a light emitting diode and/or a horn. When detected field voltage exceeds the threshold of the indicating means, a visual or audible response occurs, indicating that safe field levels have been exceeded.

Abstract: Hand-held instrument for measuring the temperature of a target without contact with the target. The instrument utilizes a microprocessor and a digital display to calculate and indicate different temperature functions. Compensation is included for the effects of emissivity and ambient temperature changes which otherwise could result in inaccurate readings. Temperature trend direction liquid crystal arrow(s) actuated by the microprocessor are included in the display.

Abstract: The ambient broadband radio frequency field strength from broadcast stations is monitored (FIG. 4) by periodic sampling (50, 52). A warning indication is provided if the field strength drops significantly. Drops in such field strength have been correlated empirically with the occurrence of seismic activity, usually several days later. Thus the indication serves as an early warning of an impending earthquake. In one preferred embodiment, a broadband, horizontal, very long monopole antenna (40) was connected to a rectifying and smoothing circuit (FIG. 3) to provide a dc output proportional to the ambient rf field. This voltage is digitized (50), and using a suitably-programmed computer (52), the digital version of the field strength signal is sampled once per minute (78). A cumulative or running average of the minute samples is calculated (80) and held. Once per hour the latest running average is stored (84) and a standard deviation (SD) of the last 24 hourly stored running averages is calculated (88).

Abstract: A system for simultaneously detecting nuclear radiation and pressure combines light signals from a radiation sensitive scintillating optical fiber with light signals from a pressure sensitive optical fiber. The scintillating fiber is coupled to a light transmitting optical fiber for long distance light transmission to a detector unit such as a photomultiplier tube. The concurrent detection of radiation and pressure of radiation and pressure is used to trigger an alarm signal.

Abstract: Method and apparatus for monitoring the opening and closing of a door and for detecting unauthorized opening of the door. The apparatus comprises a light emitting diode and a sensor mounted with respect to the door so as to be in optical communication with one another when the door is closed. A microprocessor monitors and controls the operation of the light emitting diode and sensor. When the sensor is receiving light, preliminarily indicating that the door is closed, the microprocessor verifies that the light emitting diode and sensor are still in optical communication with one another. In the preferred embodiment verification is achieved by causing the light emitting diode to emit a predetermined sequence of pulses and monitoring whether the sensor tracks the predetermined sequence of pulses. An alarm signal is provided when the sensor senses light and the microprocessor determines that the light emitting diode and sensor are not in optical communication with one another.

Abstract: This security system monitors a remote intrusion-sensing unit by probing it with a probe signal that is randomly modulated. The intrusion-sensing unit replies with a composite signal in which "secure" or "alarm" status information is superimposed on the random modulation of the probe signal. (The system may if desired be elaborated to accept and utilize other status information, such as "access" or "reverse correlation.")A master unit checks the correlation of the reply-signal modulation with the probe-signal modulation, and generates a special "deception" alarm if the correlation is not in accordance with an established pattern--such as positive correlation, reverse correlation, or correlation varying in some way that is systematic or otherwise determinable by the master unit.

Abstract: Method and apparatus for testing microwave oven cavities during the oven fabrication process after the cavity forming operation is complete. The cavity to be tested is positioned front frame resting on a test plate containing a non-protruding microwave power source and choke/ferrite attenuators. The power source radiates into the interior of the cavity and microwave leakage is measured at the cavity exterior.

Abstract: A modular field strength measuring and indicating instrument that includes as one component a sensing module with a sensitive D'Arsonval meter movement and a receptacle for interchangeable plug-in type sensing modules for measuring an electrical condition, such as electrical power. The other component is a field strength sensing module that plugs into the receptacle and which includes a self-contained DC voltage source, a sensing antenna, a high-impedance, variable gain, linear DC amplifier operatively connected to the voltage source for amplifying the field strength voltage signal sensed by the antenna, and circuitry for transmitting the amplifier output voltage signal to the D'Arsonval meter movement for indicating the field strength detected by the instrument. The field strength sensing module may be used in the meter module interchangeable with other modules, such as modules for measuring RF power in RF transmission lines.

Abstract: An apparatus for the identification by microwaves of a sheet article composed of an electrically non conductive material, the article being marked for identification by the incorporation therein of electrically conductive fibers. The apparatus comprises at least two microwave emitter devices one adjacent the other with detectors for the waves reflected by the article when advanced before said devices. The apparatus comprises also detectors for the waves transmitted through the article and placed in front of said emitter devices. Regulating methods of the apparatus are also described for raising the sensitivity of the identification signals through setting of the distances between the emitter devices, detectors for transmitted waves and support for the interposed article.

Abstract: An apparatus for the identification by microwaves of a sheet article composed of an electrically non-conductive material, the article being marked for identification by the incorporation therein of electrically conductive fibers. The apparatus comprises: at least two microwave emitter devices one adjacent the other; detectors of waves reflected by the article when advanced before said devices; a screen placed in front of at least one of the emitters; and, regulating means for raising the sensitivity of the identification signals by setting the distances between the emitter device, screen and support for the interposed article.

Abstract: A warning device to be incorporated for giving a warning or attention-getting statement in synthesized human speech to call the attention of a photographer to the need to correct the condition of the camera. The warning device includes a power supply which is adapted to operate upon receiving a warning signal provided corresponding to the occurrence of a camera condition to be warned against and a delay circuit for delaying the warning signal. The power supply is adapted to allow the power supply to an amplifier connected between an acoustic signal generating circuit and a speaker immediately upon receiving the warning signal. The delay circuit directs the warning signal to the acoustic signal generating circuit with a certain delay time at least equal to the time in which the amplifier becomes stable in its operational state for the successful synthesis of acoustic signals.

Abstract: There is disclosed a seal system for materials where security is of the essence, such as nuclear materials, which is tamper-indicating, which indicates changes in environmental conditions that evidence attempts to by-pass the seal, which is unique and cost effective, said seal system comprised of a seal where an optical signal is transmitted through a loop, with a detector to read said signal, and one or more additional detectors designed to detect environmental changes, these detectors being operatively associated with the seal so that detection of a break in the optical signal or detection of environmental changes will cause an observable change in the seal.

Abstract: A passive infrared intrusion detector is configured to resemble an electrical wall outlet. The unit includes a light for visually indicating the direction of its beam of sensitivity, and a lens unit which facilitates directional adjustment of the beam.

Abstract: A portal radiation monitor combines 0.1% FAR with high sensitivity to special nuclear material. The monitor utilizes pulse shape discrimination, dynamic compression of the photomultiplier output and scintillators sized to maintain efficiency over the entire portal area.

Abstract: A security device for determining the opening or closed condition of an access gate, such as a door or window hinged within an opening in a wall, has a detector unit mounted on the wall adjacent to the opening and linked to a remote control unit by a radio transmitter in the detection unit and a radio receiver in the control unit. The detection unit has an infrared generator and an infrared detector isolated from the generator, the detector and generator confronting a reflector mounted on the access gate when the access gate is closed. The reflector is translated from the field of the infrared generator when the access gate is open. The infrared generator is excited by a pulse generator to produce pulses of infrared radiation, and the scattered radiation from the reflector is detected by the infrared detector to produce electrical pulses coincident with the pulse generator.

Abstract: A self-contained photodetector for detecting the light flash from a photoflash unit which is supposed to flash when the shutter of a camera opens. The detector has a light-activated SCR for turning on an IC chip timer, which produces an output signal that turns on a transistor and causes a piezoelectric buzzer to produce an audible signal. All these components are powered by a battery which is contained in the same housing with them. This housing has an opening for passing light onto the SCR.

Abstract: A train monitoring system for detecting hot boxes, dragging equipment and the like at the rail site, determining the location on the train of a monitored defect and annunciating the defect and location from a digital automated voice generator to the train crew as well as along a telephone line to a central location. Recording of the defect with time and date of same is provided. The system also has provision for self check via an external simulated train.

Abstract: A personnel electronic dosimeter includes a neutron-proton and neutron-alpha converter for providing an electrical signal having a magnitude proportional to the energy of a detected proton or alpha particle produced from the converter, a pulse generator circuit for generating a pulse having a duration controlled by the weighed effect of the amplitude of the electrical signal, an oscillator enabled by the pulse for generating a train of clock pulses for a time dependent upon the pulse length, a counter for counting the clock pulses, and an indicator for providing a direct reading and aural alarm when the count indicates that the wearer has been exposed to a selected level of neutron dose equivalent.

Abstract: An intruder detection system wherein light pulses are fed from a light source to a detector via a transmitting optical fibre, an optical terminator and a receiving optical fibre, both fibres being either stepped index fibres or poor quality graded index fibres. The fibres are disposed in intimate contact throughout their length within a cable, and compression of the cable at any region of its length sufficient to cause microbending permits light pulses to breakthrough from one fibre to the other. The time interval between arrival at the detector of a light pulse received from the source after passage through the total length of the transmitting fibre and the receiving fibre, and arrival of a breakthrough pulse received after passage through the fibres only so far as the region of microbending and back again, is indicative of the location of the compresion. The cable may be laid around the perimeter of a site to be guarded so that compression will occur when an intruder crosses the cable.

Abstract: This invention relates to a digital radiation dosemeter comprising a detector (12) converting the ionizing radiation to electrical impulses and an electronic survey device (14) for the storage of said impulses in a dose radiation counter (18). An optoelectronic transmitter (34, 38, 40) sends the informations to an external data processing system. A binary counter (42) operates said transmitter and cooperates with a reading control circuit (43)including a photosensitive receiver (44)connected in series with a magnetic reed switch (46).

Abstract: A fire sensor discriminates between fires and the flash caused by a projectile piercing the wall of a protected area. The sensor system comprises first and second radiant energy detectors, each sensitive to radiation within different spectral bands. Each detector is coupled to a control signal means for generating a control signal when the radiation sensed exceeds a predetermined amplitude. A third control signal means is responsive to the first and second detectors, and is operative to generate a third control signal whenever the ratio of the amplitude of the energy sensed by the first detector to the amplitude of the energy sensed by the second detector is less than a predetermined value; not generate the third control signal whenever the ratio of amplitude exceeds the predetermined value; and delay generation of the third control signal for a predetermined period of time after the ratio of amplitudes falls below the predetermined value.

Abstract: A liquid crystal film pack for detecting leakage from a microwave oven by passing the moist film pack adjacent the joints and seams of the oven to produce a color change in the liquid crystal material in response to a microwave radiation leak.

Abstract: Apparatus for measuring the ambient light intensity of a monitored area during consecutive time intervals whereby an indication is given whenever the difference in any one of these measurements and the immediately preceeding measurement exceeds a predetermined value. The output signal of a suitable light sensing device such as a photocell is converted to a pulse train having a frequency proportional to the ambient light level and supplied to one input of an AND gate. The other input of the AND gate is connected to receive consecutive, equal duration, timing signals generated by a one shot timer circuit controlled by a microprocessor. The output of the AND gate supplies a finite number of pulses to a pulse counter, also controlled by the microprocessor.

Abstract: In an array of coke ovens each including a plurality of combustion chambers having a plurality of flue nozzles, a measuring car equipped with a temperature measuring member runs above the array in a direction of the array or in a longitudinal direction of the combustion chambers so as to detect thermal radiations passing through the flue nozzles to measure combustion chamber temperature. The measured temperature is sent to a remote control room through antennae. Where a coal charging car of a Rahmen construction is used an antenna is also provided for the coal charging car so that even when the measuring car runs beneath the coal charging car, radio communication can be assured. The temperature of the combustion chambers can be readily and accurately measured by linearly running the measuring car whether combustion is effected in one or the other side of the combustion chambers.

Abstract: There is disclosed apparatus which is inserted in an electrical circuit, such as, for example, between an incandescent lamp and the socket therefor, to provide automatic disconnection or opening of the circuit after a predetermined time period and which includes an acoustically activated abort means to interrupt the disconnect cycles and means to reset the cycle for another predetermined time period. The apparatus may be installed, as mentioned, between an incandescent lamp and the socket therefor, installed in a common wall switch, incorporated into a common appliance receptacle or plugged into a common electrical outlet between the outlet and an electrical appliance or a lighting system.

Abstract: A fire and/or heat detection system comprises an optical fibre which is either unsheathed or sheathed in a transparent material such that U.V. or I.R. radiation in the vicinity of the fibre passes through the skin into the body of the fibre. Means are connected to the ends of the fibre to measure these radiations.

Abstract: An infrared intrusion detector, utilizing as a sensor element a pyroelectric detector element, accomplishes evaluation of the output signal of the detector element with a charge amplifier, for instance by means of a capacitive feedback coupled operational amplifier, the output signal of which is reset at certain time intervals. The evaluation circuit operates independently of the detector capacitance and therefore enables optimum utilization of the pyroelectrical properties. By virtue of the short-circuit operation and the low ohmic properties of the circuit there is obtained a particularly good non-sensitivity against external disturbances and low noise and increased sensitivity.

Abstract: A discharging element energizing circuit for a discharge-type fire alarm sensor unit including a discharging element, wherein a power supply circuit gives a power voltage to the discharging element in the form of periodical output pulses making same ready to discharge and a feedback circuit is provided to supply a feedback signal obtained from the discharging element to the power supply circuit so as to vary the interval of the output pulses. The sensor unit is continuously sensitive to ultraviolet rays only caused by a fire disaster, thus preventing a malfunctional alarm. Power consumption is reduced considerably, allowing the unit to be operated with commercially available dry cells.

Abstract: Photoelectric type detector responds to radiation in a narrow wavelength band characteristic of a fire or explosion, and a slow-response detector, such as a thermopile, is sensitive to radiation in a different narrow wavelength band centered at, for example, 4.4 microns, again characteristic of the same fire or explosion. The electrical outputs of the detectors are fed into a ratio unit which causes an AND gate to produce a fire or explosion indicating output only when the ratio of the output of the thermopile detector to the output of the other detector exceeds a predetermined value.

Abstract: A method of producing an identification signal for a sheet article of non-conductive material, which article is marked for identification purposes by the incorporation therein of a small quantity of very thin conductive fibers which are capable of absorbing and reflecting certain substantial proportions of microwave radiation energy impinging thereon, which comprise placing the part of said article in which the very thin conductive fibers are incorporated in the path of an unguided microwave beam, measuring the excess of microwave radiation energy arrested over the energy reflected and producing an output signal which is representative of the presence of such excess.

Abstract: An optical detection device particularly suitable for use in a bank note counting apparatus is provided. By the use of the optical detection device of this invention, the influence of dust or change in power of the light emitting element due to change in temperature or other factors is excluded to maintain the quantity of light received by the light receiving element at a constant level. The control circuit incorporated in the device of this invention includes a comparator for comparing the quantity of light actually received or sensed by the light receiving element with the pre-set value to generate an output signal instructing to stepwisely lower the power of the light emitting element. In actual operation, the power of the light emitting element is firstly raised to the maximum value and then stepwisely lowered to the same value as that pre-set by the operator.

Abstract: Apparatus for detecting electric fields and providing an indication of their magnitude includes a glass bulb containing a gas such as neon. When the bulb is placed in a time varying electric field, pulses of electromagnetic radiation are generated within the bulb. The number of pulses is proportional to the magnitude of the variation in the electric field. The pulses are transmitted by a fibre optic bundle to detection and recording apparatus to provide an indication of the magnitude.

Abstract: Closed loop fiber optic link means, transferring energy from a radiant source to a receiver, includes serially connected fiber optic links and detectors. Energy cessation causes alarm. Detectors include: (1) A pair of optical transducers oriented whereby light, air transmitted, is received with insignificant loss. In water, light received is so insignificant that energy to the receiver ceases. The first transducer provides a light beam within a constant index of refraction medium to the second transducer spaced and oriented to ordinarily receive the light beam. When light passes through media having different refraction indices at non-normal angles, light is refracted whereby receiver energy ceases. The transducers are oriented in a straight inclined path. (2) Optical fiber, stable to approximately 135.degree. F., which melts above approximately 155.degree. F., provides fire detection. (3) A bimetallic element attached to one of axially aligned optical fiber holders, when heated, mis-align the fibers.

Abstract: An improved dual-sensor infrared intrusion alarm system includes a motion discriminator that renders the system responsive to only radiation-emanating objects that are moving through the system's scope of surveillance. A positive or negative sensor signal is developed depending on the relative amounts of radiation impinging on the sensors. A switching amplifier selectively discharges one of two capacitors depending on the polarity of the sensor signal. The voltages across the capacitors are coupled to the inputs of a voltage comparator and the capacitor recharge time constants are selected so that an alarm is indicated only when the length of the time interval between the occurrence of a sensor signal of a given polarity and the subsequent occurrence of a sensor signal of the opposite polarity is within prescribed limits, for example, two seconds.

Abstract: To provide security against unauthorised crossing of a boundary, at least one fibre-optic wave-guide extends along the boundary. Light is directed into one end of the guide and the light leaving the guide is detected by an optical detector. An indication is given when the optical intensity of the detected light falls below a predetermined threshold, so as to warn when the wave-guide is disturbed significantly or cut through.The manufacture of a strip or strand incorporating a fibre-optic wave-guide and for use in a security system is also disclosed.

Abstract: An apparatus designed for monitoring the administering of ultraviolet therapy, particularly for portable use such as at the beach, has a control system adapted to monitor the instantaneous intensity of the ultraviolet light received by a subject being treated, wherein the instantaneous intensity is integrated by means of a rechargeable electrochemical cell to measure the total ultraviolet energy per unit area received by the subject during a given time. The apparatus is so controlled that when the total energy received by the subject as measured by the apparatus reaches a predetermined preset value as determined by the discharged state of the electrochemical cell, a warning signal either visible or audible is given to the subject. In an improved embodiment an electronic means is used to subtract the energy measured at one wavelength from the energy measured at other wavelengths, thereby providing a low cost filter means for selecting the desired wavelength to be measured.

Abstract: A device responsive to infrared radiation can control a current line to such items as interior lighting or room air conditioners in order to activate these items in response to the presence or absence of a person within their service area. The device includes an infrared detector comprised of a thermopile formed by thin-film techniques for producing detection signals amplified by a series of amplifier stages having filters passing only signals corresponding to motion of a human body. The amplified signals are led to the reset port of a timing circuit which will open the current line when no human motion is sensed within a predetermined time period. Further, the housing for the device includes a protruding neck portion carrying the infrared detector and adapted to be held by a retaining nut after insertion through a ceiling unit or the like.

Abstract: A portable microwave leakage detector comprises a dipole antenna and a hot carrier diode connected in parallel with a light emitting diode, the circuit incorporating minimum solder joints and affording maximum sensitivity without moving parts such that the detector circuit does not decay with time. The dipole antenna is oriented diagonally in a detector case so that the user of the detector automatically presents the antenna to the radiating microwave field (or leakage field) at a maximum receiving attitude with respect to the field. The detector can be utilized to determine whether a microwave oven or any other device is leaking radiation beyond limits imposed by the Food and Drug Administration.

Abstract: A battery powered device which can continuously monitor and detect nuclear radiation utilizing fully integrated circuitry and which is provided with an alarm which alerts persons when the radiation level exceeds a predetermined threshold.

Abstract: A railroad car hot box detector system is provided which includes a variable circuit means for processing the heat signal generated by an infra-red detector viewing a sensing zone along a section of track. The system includes a conditioning circuit which determines one or more conditions of the train (such as the wheel speed or temperature of the car bottom) and uses that information to vary the processing circuit to enable the heat signal to be processed optimally for the detected condition.

Abstract: A flame scanner has a sensing circuit (10) utilizing a photosensitive device (12) for monitoring and a logic circuit (20) which includes a flame detection circuit (22) and a fault detection circuit (24). The photosensitive device produces a current signal (13) indicative of the intensity of the flame. The current signal is fed to a logarithmic amplifier (14) and converted to a voltage signal (15). The voltage signal (15) powers an LED (18) with its output (4) impinging on the photosensitive device (12). The voltage signal (15) is also transmitted to the flame detection circuit and the fault detection circuit for simultaneous and independent processing. The flame detection circuit continuously processes the signal to determine if a stable flame is present, while the fault detection circuit continuously monitors the integrity of the photosensitive device and its associated sensing circuitry.

Abstract: A device for individually checking exposure to radiation is sensitive to the radiation and produces an alarm (acoustic and/or optical) when a threshold radiation dose is reached. An included time-measuring device furthermore warns the user when a surveillance period has expired.The radiation sensitive device may use an electret while the time-measuring device uses the drop in voltage of a battery occurring at the end of the discharge of the battery.

Abstract: In an infrared motion alarm an optical filter arranged in front of an input of an infrared detector is attached to a heat sink in the form of a solid metal crucible in order to reduce the sensitivity to glass-penetrating electromagnetic radiation. Changes in radiation absorbed in the optical filter are either captured in the thermal sink or decelerated at least as to the characteristic thermal radiation of the optical filter and no longer fall within the characteristic range of change of the motion alarm.

Abstract: A device for warning a person carrying or wearing it of the presence of dangerous microwave radiation is fully powered by the radiations being detected. A very low-wattage gas-discharge lamp is energized by a broadly or a sharply tuned receiver circuit including dipole antennas or one antenna and a "grounding" casing element. The casing may be largely and uniformly transparent or have different areas gradedly light-transmissive to indicate varying radiation intensities. The casing can be made in the shape of a pocket watch, fountain pen, bracelet or finger ring, etc.

Abstract: A portable solid-state radiation dosimeter provides either a cumulative reading or time base reading and includes means for generating an alarm condition when preset radiation levels are reached or exceeded. The dosimeter preferably employs a cadmium telluride crystal biased to provide a count signal corresponding to the level of radiation. The circuitry for processing the crystal signal includes a field effect transistor which provides pre-amplification, one or more stages of main amplification including noise threshold setting, and a frequency to voltage converter for essentially counting radiation pulses. One output from the converter may be an alarm signal that is tripped when a predetermined voltage is reached. Also, a digital reading of radiation count may be provided.

Abstract: A contact probe arranged to detect dislodgement of the probe from a body to which it has been attached. Probe dislodgement is detected by sensing an increased radiation level falling on a main sensor (14) located in the contact surface (10a) of the probe. The main sensor cooperates with a reference sensor (16) located in another surface (10b) of the probe which receives radiation reflected from the skin of the body to which the probe is attached. The reference sensor (16) provides a floating reference for the main sensor (14). In addition to providing an indication of probe dislodgement, the two sensors cooperate to develop an indication when they are shielded from the radiation source, thereby rendering the probe inoperative to sense probe dislodgement.

Abstract: A probe having a contact surface adapted to be placed on a body surface to monitor or control a body function. When the probe is dislodged from the body, an increased radiation level impinging on the contact surface is sensed and an indication of probe dislodgement is provided.