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