My real estate agent just bought the device yesterday. Plugged it into an outlet in my dining room and I noticed that about every 6-8 hours, the device beeps once. Then 20 seconds later, it beeps again until I press the button for it to stop beeping. Another 6-8 hours passes by and it beeps once-once again. I have other models throughout the house and they are silent. Everytimg I take it from the wall outlet, the thing sets off an alarm and wont shut up until I plug it back in again. Could it be the battery is just bad or do I have a defective unit?