PORTABLE DOOR STOP ALARM. Simply slip this portable alarm under your door. If an intruder tries to enter, a piercing 120 decibel alarm is activated. The alarm can be heard from up to 1,000 feet away. Non-skid pad prevents inward facing doors from opening. Great for home use or hotel rooms. On/off switch. Uses one 9V battery (not included). 1.8”Wx6.4”Lx1.6”D.