Abstract: A gas sensor is used for determining a concentration of a predetermined gas in a measurement volume. The gas sensor comprises a light source and a detector arranged to receive light that has passed through the measurement volume. During a first measurement period, the detector is used to make a first measurement of an amount of light received in at least one wavelength band which is absorbed by the gas. The first measurement is compared to a predetermined threshold value. If the threshold is crossed, during a second measurement period the detector is used to make a second measurement of an amount of light received in at least one wavelength band which is absorbed by the gas. The concentration of said gas in said measurement volume is calculated using the first and/or second measurement.

Abstract: A wireless sensor network comprises at least one sensor unit which comprises a sensor for sensing a parameter and at least one interrogating node. The interrogating node is arranged to transmit an interrogation message periodically to said sensor unit and to receive a reply message from said sensor unit. The sensor unit is arranged to transmit said reply message after a predetermined deliberate delay unless the sensor unit determines that an alarm condition has been met, in which case the sensor unit is arranged to transmit said reply message before the end of the deliberate delay.

Abstract: A wireless sensor network comprises at least one sensor unit which comprises a sensor for sensing a parameter and at least one interrogating node. The interrogating node is arranged to transmit an interrogation message periodically to said sensor unit and to receive a reply message from said sensor unit. The sensor unit is arranged to transmit said reply message after a predetermined deliberate delay unless the sensor unit determines that an alarm condition has been met, in which case the sensor unit is arranged to transmit said reply message before the end of the deliberate delay.

Abstract: To achieve gas detection in a precise and reliable way, but at the same time without consuming too much energy, a gas detection system is provided which generally comprises a pair of two different gas detectors. The first detector (DLP) is active continuously and sense substantially for an unspecific change in the local gas mixture. As a reaction upon the change, the second detector (DHP) of the pair is activated. This detector (DHP) performs the determination of the concentration of a specific gas or several specific gasses. The second detector (DHP) may be of a type which consumes more power, but will be active for a short period of time before returning to an inactive state where only the first detector (DLP) is active. The first detector (DLP) however is of a type using little power.