Alarm device testing using time-encoded acoustic messages

A smoke alarm device has an interface (1) with a microprocessor (2), and transistors (3, 4) controlling a piezo horn (5). The microprocessor (2) is programmed to generate a test output record including various items of data such as the device's serial number, the battery level, a contamination level if it is an optical alarm, an event log, and an installation date. This information is encoded by control of the transistors (3, 4) in an acoustic output from the piezo horn (5) using an encoding technique akin to Morse code. The data is decoded by any electronic testing device having a microphone and a processing capability, such as a PDA, a laptop computer, or even a mobile phone. Devices with stereo microphones can also be used for better performance. If the device has a camera then it could both capture the acoustic signal and take an image of the alarm device to provide a more comprehensive record. In one example, a mobile phone downloads over a mobile network an application to do this processing. In order to do an audit it is only necessary for the technician to press a test button upon which the microprocessor (1) generates the acoustic signal with audit data. This acoustic signal is captured by the testing device and either decoded by that device or uploaded to a central host for decoding and further processing and storage.