More than likely it needs a new 9-volt battery. Usually the unit will twist slightly to one side so you can remove it from the base that secures it to the ceiling or wall. Even hard wired units will have battery back-up and more than likely that is the cause for your beeping. Most have the battery compartment on the underside of the detector...sometime you'll have to remove one screw that secures the door. A few odd models have the battery is strange places...you can always try to ...»

Change the battery. If that doesn't do it, replace it. I believe the life expectancy of them is 10 years.

On most smoke detectors when they begain to beep that means the battery is low and needs to be changed. I hope this helps.

Tracey,

If it is an older model, I recommend getting a whole new replacement unit. It is one of those things that you hope you never need...but when you need it, you want it to be working perfectly. I recently replaced one with the combination fire/smoke/CO detection capability. Tim

Hi Tracy. I did a short video that maybe of some help to you. http://youtu.be/IyQEux8IKNA

Something that hasn't been addressed is if a smoke detector has gone off, it will cause an intermediate beep with the smoke detectors it is connected to. To find the guilty smoke detector, look for the one that has an intermediate red flash. It will need to be pulled down and disconnected from power for a few seconds to reset it.