The present invention relates to alarm systems and more particularly to intrusion detection systems. 
The primary purpose of known burglar alarm or intrusion detection systems is to either deter entry of an intruder or to aid in the apprehension of an intruder by alerting the authorities.  The former type systems sound a loud audio alarm upon detection of an intruder to scare the intruder away and to alert anyone in the immediate vicinity of the premises of the intrusion.  The latter type systems have "silent" alarms which provide remote signals to the police or other security agent to alert them that an intrusion is in progress so that the intruder may be apprehended.  Some systems include features from each of the above type of systems.  The known burglar alarm systems vary in cost and complexity from simple and inexpensive systems to highly sophisticated and costly systems. 
The disadvantage inherent in the above-described systems is that they do not provide an indication to an owner of the secured premises, upon his return to the premises, that a break-in has occurred during his absence.  For example, the "silent" alarms provide a signal only at a location remote from the secured premises.  The audible type alarms may be timed to sound for only a predetermined period to avoid annoyance to neighbors.  In any event, it is possible that an owner returning to the secured premises will not be alerted to the fact that a break-in has occurred or is in progress, and an actual confrontation with the intruder may result. 
Certain known burglar alarm systems do provide a visual intrusion signal at a central alarm control box.  However, the control boxes are located within the protected premises and cannot alert a returning owner to an intrusion before he enters the premises.  Thus, an actual confrontation with an intruder within the premises is still possible. 
The present invention overcomes the disadvantages of the above-described systems by providing an intrusion detection system specifically designed to generate an intrusion signal which is visible from outside of the protected premises to prevent an actual confrontation between a returning owner and an intruder within the premises.  The present system also includes a test system, operable from outside the protected premises, to determine if the system has been tampered with, as for example by an intruder, during the owner's absence.