22 blank powered perimeter alarms

[subprep]

Sub prep I don't know if this helps but simply what it does is this. There is a spring loaded nail that it held under tension by a thin bar attached to a string. When the string is pull the bar is removed releasing the spring loaded nail into the blank so it makes a noise.

Thank you, yes after reading your post and reviewing the photos I get it now :-) Just so happens I have shot hammers and .22 blanks :-) Now all I need is one or two of those sentries...

 

[Hump66]

M119 Booby trap simulators are kinda neato too.