Anti -theft chain

The utility model discloses an anti -theft chain, including slot and chain cover, run through on the lateral wall of chain cover and seted up the slide, the slide narrows down from top to bottom gradually, is equipped with the limiting plate on the inner wall upper portion of chain cover, and the limiting plate below is equipped with I -shaped bracket, wears to be equipped with automatic telescoping device on I -shaped bracket's the riser, and the lower extreme that is connected with compression spring II, compression spring II at I -shaped bracket's lower extreme passes through the lower part fixed connection of spring holder and chain cover, the one end of slot be used for with door frame fixed connection, the other end of slot is used for chain cover in with I -shaped bracket's up end cooperation downwards pressing down I -shaped bracket so that I -shaped template when moving down to an allocation through getting into behind the slide, exposes in the switch hole that the tip of automatic telescoping device