This alarm uses different sensors to detect activity inside the car. When any of them sense activity, the alarm will start making noise for a particular duration.
The alarm has a START_DELAY time which allow the user to arm the alarm and leave the car. Once this delay passes, the alarm executes a routine every PERIOD_SLEEP looking for activity in the sensors. When activity is sensed, a delay of ALARM_DELAY is used to allow manual disconnection of the alarm. After this time the alarm starts making noise during ALARM_DURATION time. After this time the alarm waits REARM_DELAY before rearming alarm again.
Setup procedure: depending on alarm battery level the starting procedure changes, indicating if everything is ok to work, if the battery needs to be replaced/charged, or if battery is so low that the system won't run:
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Correct function is advertised by BATTERY_OK_REPETITIONS short buzzes.
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Low battery is advertised by BATTERY_ALERT_REPETITIONS long buzzes, but the alarm stills running.
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Very low battery is advertised by BATTERY_ERROR_REPETITIONS short buzzes and the system won't run.