A photo would help a lot, but if it is by the floor it sounds like the propane detector. These need replacing about every 7 years or something. Like most of the safety alarms, it will start to yell at you to let you know it's time for a new one. Can't just replace the batteries on these, must replace the detector.
I feel so safe having a Wsdcam alarm, I was amazed. It was so easy to install and operate. Most wireless alarm systems work on the inside when you close the door or window and when it is opened the alarm sounds. This one you can close the door and arm it from the outside with a remote. The alarm is very loud and won't stop until you disarm it.