Abstract: A security device for controlling the ignition circuit of a vehicle provided with a steering lock 11. The device comprises an electrical circuit having: a security ignition circuit switch means CO32 for opening and closing said ignition circuit independently of any manually operable ignition circuit switch means; and a steering lock control switch means MS1 connectable to said steering lock 11 and having disabling and non-disabling operating conditions, corresponding respectively to locked and unlocked positions of the steering lock 11, for respectively disabling and not disabling said vehicle with respect to starting thereof. A plurality of user actuable first switch means 3 is arranged so that operation thereof is necessary in a predetermined sequence to close the security ignition circuit switch means CO32. An alarm connection means CO52 is connected to alarm means SIREN and arranged for activation in response to actuation of said first switch means 3 in an incorrect sequence.