Infrared Beam Burglar Alarm
Could someone please tell or show me a fairly inexpensive way to throw an infrared beam across my office and once it's tripped by an intruder an outside alarm or siren (I mean the loud ones-like you can hear several blocks away)would go off. I'm so impressed by the quality of minds on this website. I know someone can probably help. Bless You All.
Thank You So Far!