The door chain lock

Compared with a deadbolt, the door chain protects almost nothing: a determined shoulder defeats it in the time it takes to notice the gap has opened, and the screws anchoring the track are shorter, on average, than the screws holding up a bathroom towel bar. The failure mode is consistent enough to predict on sight: the track loosens first, working free of softwood doorframes not built to hold much more than their own paint, so that a chain rated to stop a stranger ends up rated mainly to stop a friend from walking in unannounced. Its actual function, then, is procedural rather than physical: it converts an unlocked door into a door that must be explained, buying the seconds a guest needs to decide whether to answer, dress, or pretend to be out. Slid home, the chain draws taut in a shallow arc between two small brass plates, and the door settles into its narrow allowance with a soft metallic complaint that is, on most nights, the last sound anyone hears before falling asleep with the television still running. It is engaged more often out of ritual than calculation, the way a seatbelt gets buckled on a driveway. Whether it has ever stopped anyone who mattered is not the kind of thing that shows up in a doorframe, and the mechanism's real record, if there is one, was never written down anywhere it could be found.

Arthur Pell