Abstract: A concealable burglar alarm system for automatically generating a warning in response to either unauthorizd opening of a window or breakage of the associated window pane. The system includes a translucent, generally rectangular sending unit which is adapted to be permanently secured upon a window sill adjacent to a window being monitored. The sending unit includes a generally planar mounting base, and an associated magnetic reed switch having a stationary portion and a pivotally deflectable portion. Relative displacement between the reed switch moveable portion and the stationary portion causes an electrical circuit to close, activating a remotely disposed electronic circuit. The base of the sending unit preferably includes an integral, outwardly extending cylindrical projection upon which the coiled portion of a reed switch activation spring is mounted and flangeably secured. The spring includes a pair of outwardly extending first and second ends which are biased apart.