Customer FAQs Discover answers to the most frequently asked questions from ADT customers with a simple click of a button. 1. How do I replace or fix my sensors? Not every system is the same. That means that not all sensors are the same. You can learn how to fix sensors by referring to your security system user’s manual.If you want to replace a sensor, call the residential service number on our Contact ADT page. An ADT representative will be happy to assist you.