There was the Pressure Switch Mat. They could be used Closed Circuit like under a large art item where when pressure was taken off mat object was sitting on broke electrical circuit and caused an alarm or more typically Open circuit where an intruder stepped on the mat under a rug and closed the electrical circuit activating the alarm.
They where also used as a back up alarm in early alarm systems which had Phase II protection as it was known so that if an intruder opened the door to a home and set of the local only alarm which means it did not call police which was common in early days .The Alarm then shut off after 15-30 minutes and if the intruder came back in the alarm would not go off as the primary loop was tripped but as soon as he stepped on the mat on the floor or stairs the alarm would go back off again.Do to Phase II protection loop which was Open Circuit
Of course there was a problem some panels only accepted closed circuit loops so they made a converter to change the mat from open to closed circuit operation for the panel by means of a sensitive relay
The mats where devious as to how and where they where being used just like the trap wires and where responsible for many burglars being caught , but also a pain dogs and cats could set them off and if they got wet from cleaning rug or water leak they shorted out and needed replaced .You always needed to male sure you arranged furniture so it was not on mat etc. One customer one time had a small roof leak and put a bucket under it and yep you guessed it the bucket filled got heavy enough and set off the alarm. Needless to say very few are still in use but still available thru United Security Products for special tasks like knowing if some one has fallen out of a chair or bed etc.
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