I have a 5192SD detector, the red light is constantly on.

That unit is an addressable device and works only with Ademco/Vista/First Alert panels that utilize a polling loop. The address would be in the form of a serial number that should be on a sticker affixed to the unit.

What alarm panel are you using and what terminals are you connected to?

A steady light indicates the panel has latched the unit in alarm. It should be flashing at ten second intervals (if I recall correctly). I don't know if connecting it to a standard 2-wire smoke detector zone will cause the symptoms you describe, but make sure you are using a polling loop and have the correct polarity.

Take it down and clean it, reinstall and see if that corrects it. otherwise replace the unit.

I would generally replace any smoke detector that acts up unless I am certain of the cause and am confident the device is not at fault and whatever did cause the problem could not have damaged the unit in any way.

But then, I am something of a smoke detector "nazi" and do not believe in toying with ANY life/safety device.

Since you didn't mention an alarm panel - on the off chance it is connected it to a 110vac household smoke detector circuit, remove the device immediately and throw it in the trash. I only bring that up as I have seen ONE time where a guy got hold of some low voltage smokes and tried to use them on his 110 house ckt. However, I'm pretty sure that you wouldn't have a constant red led in that case and the smell should have alerted you to the issue fairly quickly.

Hi,

You omitted to mention on what type of security or fire system this unit might be on. If it is on a regular security system and the unit was activated at one time, depending on what type of system it is on, you could just reset it by turning off your system one more time or there may be a smoke reset button on your keypad. Ademco/Honeywell's systems will reset after you turn your system off twice. A DSC has a smoke reset button right on the keypad.

If after resetting of the system the smoke light is still on, call a security professional to deal with it. Hope this helps you.