Most washing machines use a wax motor to lock the door, it heats up wax to cause it to expand when it melts, which drives a pin. They're fairly failsafe as if you kill power, they will open no matter what.

Latching relays/(technically solenoid) could be driven on/off fast, the downside is in a power cut or an emergency, the relay wouldn't release unless specifically driven so.

So the third option is a momentary solenoid, which would need to be powered the whole time the door is shut, and they require a surprisingly significant amount of power. Typically 10-20w. Negligible when it compares to the KW+ heating elements, but they do add up for the energy ratings..

Fwiw, I currently have a haier, which does have one of the second options, and opens immediately after a wash and it's amazing. Can't go back.

But, wax motors continue to be used because they're just the right tool for the job.

> how to open that damn thing

"I'm sorry Dave but I'm afraid I can't do that"