Google Nest Detect
Stick Nest Detect on a window and you will know when it opens. Stick it on a wall and it senses motion in a room. Stick it on a door and it can do both. With Quiet Open, you can open a door while the house is armed, without setting off the alarm. Requires a Nest Secure alarm system starter pack.
Google Nest Detect is powered by using either Panasonic CR123 or Energizer CR123A lithium batteries that are widely available. We recommend replacing them every year on Labor Day along with all your other battery backup replacement strategies.