This compact motion sensor will detect anyone who attempts to enter the protected area. If motion is detected a powerful 130 dB alarm will sound to scare off the intruder and alert others to your need for help. The owner may arm or disarm the unit using a programmable security code. Ideal security for home, retail store, office, or hotel room. Requires four AA batteries that are not included. This unit measures 6 1/4 inches x 2 1/2 inches x 1 3/4".