A lock is a mechanical device for securing a door, chest, or other receptacle so that it can only be opened by an authorized person. Most locks are opened by a key which is placed in the lock and turned. Combination locks do not use a key but rather have a cylinder that is turned to certain stops. Today, many hotels use special plastic cards with magnetic strips as keys which cause a door to open electronically when inserted in a slot near the doorknob.
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