I created a new version of the Zigbee multi function device. It is used to signal (by email) the status of my lawn mower (a Robomow RM400). The base station of the mower powers the mower when it is in the base station. This is done by applying 30 Volt to the 2 pins with which the mower is connected to the base station. When the mower leaves the station this voltage is withdrawn and drops to a few volts.
Using this voltage (via a converter/filter) as an input to the Zigbee module, leaving and returning of the mower can be used to transmit the status to my home automation software, which in turn sends an email to my email address.
After the mower has finished with mowing the edges of the lawn (programmable), it will first return to the base station, leaving it immediately again to start the real mowing. Without measures, this would mean that the leaving/returning is signaled twice. By adding a 1 minute delay, and checking again, this can be overcome.