SIGGEN

1. automatically: signal generation is initiated by a self regulating mechanism such as a timer or light sensor.
2. by wave action: the signal is generated by the motion of the sea surface such as a bell in a buoy.
3. by hand: the signal is generated by a manually operated mechanism such as a hand cranked siren.
4. by wind: the signal is generated by the motion of air such as a wind driven whistle.