Abstract: A commentary system for exhibits at museums includes a recorded commentary store and an output amplifier which supplies the recorded message to an aerial. Visitors to the museum are provided with a pick-up coil and an earphone connected directly to the coil. The coil is placed firmly closely adjacent the aerial to inductively couple the aerial and coil so that the visitor may hear the commentary. The pick-up coil and the earphone require virtually no maintenance and no power supply. The audio signal is generated solely by energy derived from the broadcast.

Abstract: A magnetic code operated lock cylinder is releasably coupled to a shaft extending into a door. When the lock is unlocked a pinion gear is rotationally coupled to the shaft which shaft on rotation retracts a door latch. The gear is coupled by a toothed rack to a gear connected to a handle. The handle and rack are surface mounted on the door.

Abstract: A magnetic key operated lock has an anti-rap arrangement which comprises a magnet pin supported in a bar mounted in a slide member. The remote end of the pin fits into an aperture in a locking plate and is pivoted to swing downwards out of the aperture when a correctly coded key is inserted into the lock. The correctly coded key has a repelling spot to pivot the magnet as required and before the key attempts to move the slide member from its locked position. Rapping on the face of the lock cannot move the remote end of the magnet pin out of the aperture because it is restrained by its pivoting action from moving laterally out of the locking plate. Another anti-rap arrangement includes a padlock incorporating both anti-rap arrangements.