The batteries are low in the Motion Sensor and they will probably only last for another few weeks before the sensor stops working altogether.
Take the Motion Sensor from its magnetic mount. Remove the back cover of the Motion Sensor by twisting the two halves a small amount so the solid dot and hollow dot are next to each other.
Pull the back of the Motion Sensor away from the body, you may find a thin, flat screwdriver helps to separate the two halves.
Remove the CR123 battery by pushing it lightly against the spring.
Wait 30 seconds before putting in the new battery.
Put in the new CR123 battery.
The light will flash once every second for 30 seconds.
Return the cover, push the halves together until the solid and hollow dots meet. Now twist a small amount until the two solid dots are next to each other.
Select the Motion Sensor with the flat batteryThe old number for the Motion Sensor may be on the back of the device.
Wake up the device by pressing the button on the back of the sensor once.