Master Lock Ultrasonic Alarm

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Greetings:

I would appreciate any information concerning the Master Lock
Ultrasonic alarm controller system (model 2428 is an example),
especially a description of the power line signalling method
and available devices when this product was sold.

The 2428 unit we have has a transmitter connected only to the
power line through the N.O. contacts on the alarm relay which
employs a neon-bulb relaxation oscillator to key the RF at 1HZ
when activated.  The transmitter board contains a few transistors,
discretes, a slug-tuned coil and a yellow dime-sized part labeled
"channel 4", perhaps a resonator?

The ultrasonic alarm pcb has four 1458 op-amps, two relays
and discretes; date codes ~1977

Regards,

Michael