2 of 3 began to ring every minute dice installation (a sign that the battery is delivered already worn). As it can not be changed, they are unusable. According to the label, they were made in September 2014 and are expected to last 10 years (until September 2024). If only one of the detectors was defective, I can still understand. 2 of 3 arrived already down, it's not a good sign of the quality of the product! I do not recommend this purchase.
