Abstract: A vehicle security siren that includes a rechargeable back-up battery and an electronic circuit that minimizes current drain from the vehicle's battery by controlling the rate at which the siren's back-up battery is charged by the vehicle's battery. The circuit charges the siren's battery at a relatively high rate when the vehicle engine is running or the ignition is on, and by a low charging rate at other times. This multi-level charging rate preserves the vehicle's battery charge particularly if the vehicle is not driven for any extended time period. The circuit includes a back-up battery condition detector that issues a warning signal in the event of failure of the back-up battery. The circuit also limits the maximum siren duration in the event that either the vehicle's battery or the security system is disconnected from the siren.

Abstract: An ECG electrode impedance measuring approach is utilized which can determine, simultaneously, the condition of all electrodes in a three or five lead ECG monitoring configuration. A CPU automatically selects an ECG lead configuration in which all electrodes are attached to the patient and are below an impedance threshold. If the CPU cannot select a good ECG lead configuration, then the CPU signals a total lead failure. Electrode impedance is determined by passing a small DC current through each active electrode and the current is returned via the reference electrode. A comparator tests the resultant offset voltage induced between each active electrode and the reference. If the offset voltage exceeds a fixed threshold, then a flag is set and transferred to the CPU. The CPU can change the ECG lead configuration by issuing commands to an electrode lead switching network.