I purchased a house about 7 months ago and found it had interconnected AC smoke/CO detectors that were all unplugged. Not knowing the age of them I replaced them all using photoelectric smoke/CO detectors in the basement and main floor and ionization smoke detectors in the upstairs bedrooms. All are from the same manufacturer and include voice alerts and 10-year batteries and all test good.

Just today they went off for the first time ever with a smoke alarm. Neither seeing nor smelling smoke, and possibly being stupid but not wanting to loose anything, I rushed around the house checking for smoke with extinguisher in hand and found none. I then took a closer look near each detector and found no sign of smoke or fire but did find that the detector that initially went off was in the basement. I cleared the alarm memory and ran a test with no issues.

The only thing that I can think of that set it off may have been some R-410A AC refrigerant. The AC line runs only 3 inches from the detector and my HVAC guy said a leak may be present in the line somewhere due to having to top off the AC, 2 lbs worth of refrigerant, just two months ago.

So the question is can a photoelectric smoke/CO detector detect R-410A AC refrigerant as smoke?

Also should I move the detector? It is right at the foot of the basement stairs.

Some additional information based on comments and answers given.

I put up a divider of cardboard between the AC line and the detector 2 days ago. No false alarms since. No markings have been noticed on the cardboard even though the AC has been running on and off throughout so an oil cloud is not likely. The AC has not lost any efficiency since it was filled. If it is a leak it's not a big one. The AC line has buzzed a few times so I'm going to have an HVAC company over for checks.

  • of course it can, but it is unknown if it does ... you should be directing your question to the smoke alarm manufacturer
    – jsotola
    Jul 29, 2021 at 21:32

3 Answers 3


Photoelectric smoke detectors measure the reflection of light from small particles in the air. Although the refrigerant itself is a transparent gas, there may be lubricating oil in it that caused an oil fog, triggering the alarm.

That said, it does not seem safe living with a refrigerant leak large enough to set off the alarm:

  • The refrigerant is moderately non-toxic, but read the safety data sheet: " Overexposure may cause dizziness... CNS depression and cardiac arrhythmia... and can cause asphyxiation..."
  • If there is lubricating oil, a fine oil mist is not good for the lungs.

Of course, a leak that large would require continual topping off the refrigerant, and failure to do so could destroy the system.

Since you've been in the house for less than a year, you likely have recourse to get the seller to fix this.


If there is a refrigerant leak the AC will stop working rather quickly (possibly a few weeks). The fact that it was just topped off tells me there was a leak. You should inquire where the leak was and if the leak was repaired. Refrigeration systems are sealed systems and freon does not wear out so you should never need to top off. My system has been operating flawlessly for the last 15 years no problems and still operates at capacity. If the leak is very small you may find it cheaper to top it off every year.


Don’t rule out a bad smoke detector. I installed 10 in a new construction and one was bad. Was fine for a few days then scared the life out of me. They seem to do a self test every now and then and go off. Try swapping the basement one to another location and see if the alarm stays in the basement or moves with the smoke detector. Like you I have photoelectric on main areas and ionization in the bedrooms. It too was a photoelectric that was bad and had to be replaced. Mine are all Kidde

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