Two pieces wireless magnetic contacts into one pack. Wireless magnetic contact for security, it works with wireless alarm system and Erobot smart cameras via 433MHz. The detector adopts reliable reed switch to provide reliable, false alarm free perimeter protection as the first defense line of your security system. The detector is suitable for monitoring doors, windows, drawers, safe boxes, gun boxes, cabinets etc. It's powered by 1x AA battery, power lasts 24 months (depends on battery's power capacity). The included removable bracket, allows you to take off to replace the battery, and test button allows you to regularly check the status of the detector. Additionally, it has low voltage remind feature, when battery runs out, the Yellow LED will start blinking. Due to shipping regulation, the product will be delivered without battery.