I do that sometimes for many hours while I'm out or at night while I'm alseep. I leave the cage firmly closed with a piece of thin string or scotch tape. Both can be easily broke by the slave by pushing the door from inside with moderate force in case of an emergency.

I also leave a swiss army knife inside the cage, even though pushing the door is enough (we tested it). There's also always clothing and other necessities prepared and available right next to the cage.

Caging isn't necessarily about restraining your slave. To us, the symbol is good enough... It's even more exciting for both if the slave knows that she can easily go out yet she won't do it in order to please you. Trusting a slave this way can be very profitable.