Seized & Jammed Lock Opening: before you call

It is the coldest morning of the winter and the key goes halfway into the side door and stops. There is frost on the face of the cylinder, and the door on the shaded side of the house has done this before.

Worth answering before the call

Is anyone inside, and can the door be opened from that side? Was the door painted, re-hung or fitted with new weatherstripping recently? Which side of the building does the door face, and is it near a salted driveway?

The thumb-turn is stuck from inside and we need that door to get out. What should we do?

Use another exit for now and call. From the inside the fault is usually a bolt pinned by the frame or a bent spindle, both of which the locksmith frees without damage. A main exit door should open from inside without a key or special knowledge, so the repair leaves the door doing exactly that, and if the hardware on it was the wrong type for an exit, a thumb-turn deadbolt is suggested.

Could a jammed lock mean someone tampered with it?

Occasionally, but wear and weather are far more common. Signs that point to tampering are fresh scratches around the keyway, a plug that sits crooked, or debris such as glue or a broken tool tip inside, none of which appear from ordinary use. The locksmith looks for these during the inspection and says plainly what was found. If the cylinder has been damaged that way, it is replaced and, if you wish, the other doors are rekeyed.