inventions
Instead of a key, you can hold a small circle of metal or plastic against a machine, and the door clicks open all by itself.
An automatic lock is the name for a lock that opens on its own when the right signal is given, such as holding a special card or key fob near it, instead of needing a traditional metal key turned by hand. Inside, a small sensor checks the signal, and if it matches, a mechanism releases the door so it can swing open.
A paintbrush is used for painting pictures and a balloon is filled with air for fun, and neither one has any connection to locking or unlocking a door, so they clearly don't fit the description.
Many hotels, offices, and even some houses now use these automatic locks because a lost card can simply be deactivated and replaced, unlike a lost metal key, which might mean changing the whole lock.
inventions
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