My parents still live in the house I grew up in which has a central vacuum cleaner.
Theirs is a “Beam” system.
Each outlet has a copper pair of wires running to it, connected to two contact pins on the inside of the outlet, and the vacuum hose has a metal ring on it so that as it’s inserted, it completes an electrical circuit between the two contact pins, signalling the vacuum cleaner turn on, once the circuit is broken, it would turn off.
Perhaps the system you had actually worked like this.
Theirs is a “Beam” system.
Each outlet has a copper pair of wires running to it, connected to two contact pins on the inside of the outlet, and the vacuum hose has a metal ring on it so that as it’s inserted, it completes an electrical circuit between the two contact pins, signalling the vacuum cleaner turn on, once the circuit is broken, it would turn off.
Perhaps the system you had actually worked like this.