Security & Fire Protection Systems/Replacement for Firex 120-538C


Hello, What would be a good replacement for our Firex 120-538C alarms?  They were installed in our house when it was built in 1997.  Thank you.

Hello Dave, and thanks for your question.

The Firex brand was absorbed by a competitor several years ago, but they've done a good job in trying to make detector replacement easy.

Here's the closest match I found for your old detectors:

The advantage here is that they supply an adapter that allows you to plug in the new detector using the old wiring harness.

On the other hand, you could use any 120-volt detector with battery backup, and just have to rewire the harness.

I hope that helps!

Best Regards,


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Dave Neuweiler


The design and application of burglary and fire systems for homes and businesses. Helping alarm owners understand how their system works. Helping to troubleshoot false alarm problems. Questions about monitoring issues.


Over a quarter century in the industry. Experience in installation, service, and monitoring centers. Training manager for a national protective services company; director of education and training for a national trade organization for for alarm dealers.


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