A security tag includes a tag body member, a connecting member releasably engageable with the tag body member, and a locking member having a locked position in a first thermal state configured to lock the connecting member to the tag body member, and having an unlocked position in a second thermal state configured to unlock the connecting member from the tag body member. The locking member includes a locking body comprising a shape memory alloy, and a clamping member connected to the shape memory alloy. A transition of the shape memory alloy element from the first thermal state to the second thermal state moves the clamping member from the locked position to the unlocked position, thereby enabling the connecting member to be detached from the tag body member.