After checking to see if your make and model is recalled, did the electrician suggest 'blowing' the sensors clean? Perhaps that can be done. You may want to buy a can or 2 of compressed air. (Don't use the back-side of a vacume cleaner - It may blow dust.)
Anyways, you can still contact the mfgr. to see if they have any ideas. Visit FirstAlert.com. My best to ya and hope this helps.