wirele doorbell alarm Warm prompt:1. Not only the product is a doorbell, but also it is a home alarm system.2. DB_A1,A2,A3 support 433MHz detectors, but not support wifi function.3. DB_B1,B2,B3 support 433MHz detectors, also support wifi funtion. The best recommend !!! How to choose a best doorbell? 433MHz Version For model: DB_A1,A2,A3 Wifi & 433MHz Version For model: DB_B1,B2,B3. Wirele door detector Wirele infrared detector Product include DB_A1: 1 normal doorbell alarm host + 1 button.DB_A2: 1 normal doorbell alarm host + 1 button + 2 wirele door detector.DB_A3: 2 normal doorbell alarm hosts + 1 button.DB_B1: 1 wifi doorbell alarm host + 1 button.DB_B2: 1 wifi doorbell alarm host + 2 buttons.DB_B3: 1 wifi doorbell alarm host + 1 button + 1 door open detector + 1 motion detector.Due to aviation restrictions, the buttons and detectors do not contain batteries. They use 3V CR2032 batteries. To my dear customer Thank you very much for your recognition of our products and support for the store.If you are satisfied with our products or our services, please give us a precious five-star. Thank you very much!If you are not satisfied with our products, or you can't find your package, please