This car alarm was obtained in a Signetics documentation from the 1980s. The circuit uses the 555 and has a pulsed output to activate a relay that controls the horn. The sensors are parallel connected.
This circuit is from a 1997 publication, but it can be assembled with a BD136 for TR1. The...
We found this circuit in Motorola's 1990 Linear Databook. The component used is unusual. The...
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...