A key factor in the security of any door, shutter or hatch is the ability to control that accessway. A lock is the simplest and most recognisable form of control and has been used for centuries. Electromagnetically actuated locks with a solenoid at their core have been around for decades. They have changed little in 50 years or more. As an example, one proven design that found early favour in the UK was a solution to automatically lock the doors of GPO vans. More mature readers will remember the GPO as responsible for Royal Mail and the national telecommunications service (which became BT in 1980).
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