Got a cheap wireless alarm sensor to work on an old wired panel with a simple relay trick

Had a customer in a old house near downtown who wanted to add a window sensor to a new window but didn't want to run wire through finished walls. Their panel was a basic hardwired system from like 2005. I grabbed a wireless sensor from the hardware store for $18, wired the relay output to one of the spare zones on the panel, and it worked first try. No transformer issues, no false triggers. Has anyone else found a simple way to mix wireless into old hardwired setups without buying expensive converters?

3 comments

3 Comments

jamiew5321d ago

Yeah, that cat thing is funny but also kinda tells me you might have the relay wired wrong. If the sensor is normally closed for the window being shut and the relay is set up the same way, a cat walking by shouldn't trigger a zone unless the relay coil is being energized by motion. I've seen guys use a SPDT relay and accidentally wire to the normally open side, so any power fluctuation or pet movement that messes with the sensor can trip it. Check if your sensor has a tamper switch that's closing the circuit when the cat bumps the housing. That's a common gotcha with these cheap units.

elliot_johnson3122d ago

I tried something similar last year with a garage door sensor and it worked great until my cat set it off at 3am chasing a moth. Ended up having to adjust the sensitivity because apparently my cat weighs exactly the same as a window opening. Still way cheaper than buying one of those fancy retrofit kits that cost more than the panel itself.

williamb2921d ago

My mom's house had a crusty old DSC panel from 2007 and I did the same thing with a Honeywell wireless sensor. @jamiew53 is right about checking the relay wiring, I had a brief scare with a false alarm from a raccoon until I realized the tamper switch was loose. Honestly it's been solid for two years now, just had to tape down the tamper so only actual movement triggers it.