Keep your home/office safety:wireless portable door sensor alarms offers a generous detection area of nearly 160 feet. You could hear doorbell chime as visitors or guests arrive to your home, store, office etc. It sounds to notify you someone enter into, or alert you intruder trying to entry your home. Or remind you when your Children/Elderly or Dementia Patients open the door/window and sneak around. . Multiple melodies&Loud chime-The receiver Unit has 58 ringtones for your choice. 5 adjustable volume levels from 0 dB to 110 dB. . Easy to use. No wiring, just put 3 AAA batteries (included) in the receiver,tear the double-side adhesive tape of the Door / Window sensor and stick them to any door or window.The magnetic sensor activates when door and window separated. . The battery receiver is portable,bring it with you everywhere by keeping it in pocket/bag. . Customize and Expandable. Each receiver can work with 20 door window magnetic sensors, each transmitter can pair with 20pcs receivers and set to different or same music. 100 Days Full Refund or Replacement (If the order is over 30 days, please contact us by email.).Not satisfied with our product? Return it to us within 100 days and get 100% of your money back!