TS-3A is a permanently installed glad hand lock designed to secure unattached and unattended trailers while on yards, in drop lots, in transit, on client sites or in rail yards. The device is a simple mechanical air locking valve that is engaged when the there is no air in the trailer brake lines. Upon disconnecting the trailer, the driver turns the key moving a ball valve in place so that no air can be re-introduced into the lines to raise the brakes. TS-3A is plumbed directly into the air lines and requires a considerable amount of time to circumvent. Unlike a portable glad hand lock which can be removed along with the fitting, TS-3A cannot be removed without doing damage to the lines, thereby disabling the trailer’s brake system. Easy to operate and extremely secure, TS-3A has tremendous deterrent value against theft. It can be quickly installed on most air brake equipped trailers, attached either to the facing of the trailer or on the undercarriage in a concealed, but accessible, location.