A gate-locking device is a type of mechanical fastener that is used to secure a gate or door. The most common type of gate-locking device is a LATCH, which is a simple mechanism consisting of a bar or plate that fits into a notch or slot in another bar or plate. When the LATCH is engaged, it prevents the gate or door from being opened. Latches are typically made of metal and can be operated manually or with a key.