Abstract: A portable security lock of the "U-bar" type includes a rigid "U" or "C" shaped security bar (8), and a flexible security loop (14) and a generally tubular cross member (2). The cross member has a pair of sockets each of which is adapted to cooperate with a suitably shaped end of the security bar or loop, and an internal rotatable barrel member (26) having keyhole slots (28, 30, 32) which receive the shaped ends in a first rotational position. The barrel member is then rotated to a second position in which the shaped ends are locked into the cross-member. Electrical contacts connect the barrel to an alarm via the security loop so that the alarm is triggered if the security loop is removed or broken while the alarm is set.