Safety Technology International, Inc. STI-6400 Exit Stopper Multifunction Door Alarm, Helps Prevent Unauthorized Exits or Entries Through Emergency Doors Highly visible "stop sign" design acts as a deterrent Virtually indestructible polycarbonate housing Detects both unauthorized exits and entries Less expensive than heavy horizontal bar type units 3 year guarantee against breakage of polycarbonate in normal use (one year on electro mechanical and electronic components).