Motion sensor?

Hi,
I own a three family tennament in Mass.The 2nd floor stairs going out have a ceiling light,wich is operated by a motion sensor
pointing towards the stairs,so any movement turns on the light.
recently I noticed it isn't operating right,it clicks to shut off,then instantly turns back on again?this repeates constanly.I tried adjusting the sensativity,etc,but it still does the same thing?
There isn't anything moving to set it off?
Any ideas?Iam not sure how old the unit is,it doesn't look to old.
Are theseeasy to replace?The motion sensor is attached to a electrical box on the ceiling.Thanks

 

Did someone recently change the bulbs in it?

 

remove motion sensor, change to fluorescent bulbs using 25% of incandescent, last for years -- be sure to have two for redundency -- do same for outdoor lights

 

The motion sensor should be easy to replace. Perhaps the hardest part will be safely reaching the box where it is installed. Please be careful where you place your ladder.

You should be able to simply disconnect the old motion sensor and replace it with a new one. Make a drawing of which wires connect and where they connect on the old one. You may even want to mark the wires with tape or something as it is likely you will have two black and two white wires in the box.

Keep in mind that many motion sensors (especially inexpensive ones) will only work with incandescent lamps, so replacing the motion sensor and switching to a fluorescent bulb is probably not going to work.