Ring motion detector false alarms

I have two motion detectors that work normally when I test them. When I arm the system they detect motion immediately and set off the alarm. They are both in the corners of each room 8 feet up on 10 foot ceilings. No ceiling fans on (when I tested for motion with the ceiling fans on they are not detected). Sensitivity is set to low. No pets in house no balloons. . Help! Thanks.