This alarm functions as stated in the instruction book (inside the package), but is severely useless. There is actually a 30 second delay before the alarm sounds once motion is detected. To make matters worse, once motion is detected, there is a brief (1/4sec) chirp and a flashing red light that gives away the position of the device. So...effectively, if an intruder can take out the batteries (or stuff it under a pillow) in 30 seconds, your security system is compromised. What were they thinking when they made this? The door chime mode is useful (chimes immediately), but the alarm is not.