Diagnosis
This is almost always caused by a loose or compromised brush head. Vibration from household appliances or settling can trigger the motion-sensitive switch.
How to Fix It
1. Remove the brush head. 2. Inspect the rubber O-ring on the handle's drive shaft for damage or debris. Clean it. 3. Firmly press a brush head onto the handle until you feel and hear a distinct click. 4. Test by giving the handle a light tap. It should not activate.
If That Didn't Work
The problem is the internal motion switch. Store the brush separately from the charging base when not in use. If it activates while off the base, the switch is faulty and the handle requires service.
Heads Up
Do not store the brush with a travel cap clicked into place unless the handle is completely dry. Condensation inside the cap can create a conductive bridge that triggers the switch.