Hotel keycard switches on 5,000W load when placed in its holder. How does it do that?
The keycard most likely operates a contactor, which is a power switch with auxiliary coil for remote open/close. A bit heavier built than a switching relay - the contactor is expected to carry much more current than a switching relay, and the design must account for this.

The construction and appearance of a contactor is comparable to a miniature circuit breaker (MCB). The difference is that an MCB is designed to break fault currents (10,000 A), but a contactor is only designed to break load current (~ 10A.)

No semiconductor electronics involved.



Typical contactors in the 4-40 A range are made by Schneider (i.e. Telemecanique, Square D, Clipsal), Sprecher &amp; Schuh, and others.

In your application (domestic/commercial) you would be using single-phase AC power and thus a two-pole contactor.

Here are a few types:


Telemecanique 2-pole 16A contactor GC1620M5 - 2-pole for switching of single phase AC loads. Datasheet. Comes in 16A, 25A, 40A, 63A, and 100A versions. This is probably the closest to what you have.


Tesys K - 3/4 pole version for three-phase circuits


Sprecher &amp; Schuh CA8 -  3/4 pole version for three-phase circuits



EDIT:

I remembered that my room on college used to be equipped with a magnetic keycard reader, which controlled the lights and air conditioning.

The particular device used was the Enkoa iSwitch, magnetic stripe card reader model. The data on the magnetic stripe was particular to each room. (There were also RFID models.)



The datasheets don't seem to be available any more, but I had downloaded them a few years ago. The iSwitch appears to integrate two relays - one a power relay rated 10 A 240 VAC, for the room lights, and the second a volt-free contact, for signalling the air-conditioner controller. The wall socket-outlets were powered regardless of keycard.

The above information about contactors would apply when the keycard was required to control substantially more than 10 A of load.