The Gigaset Elements Alarm system L is controlled via the app on your smartphone (iOS and Android). The set consists of a base station, motion sensor, siren, IP camera, and 3 magnetic contacts. Want to expand the set? You can, up to as much as 25 sensors. Take, for instance, the extra IP camera or water sensor. When it detects something, you'll receive a notification in the app. The base station runs on AC power. The individual sensors work on batteries. That means you're free to place them where you want. Do keep in mind that the range between the sensors and the base station goes up to about 50 meters.