The use of wire barriers (tripwires) to activate military or hunting devices is widely known. Previous work by Peters and Drurnm (2; cf. 1, 3 ) has indicated that visual detection of tripwires is rather poor, and depends primarily on height of wire from ground in relation to available concealment or blending rather than upon length of wire. Once the wire is tripped, however, activation of the mine, flare, or trap depends upon the force applied to the wire and transferred to the control mechanism. In order co optimize the setting of the control mechanism, a force must be chosen rhar is high enough to prevent accidental activation by natural objects (branches, small animals, wind, etc.) yet low enough to prevent the intended victim from detecting the wire before activation. This paper reports the results of a recent preliminary investigation of the tactical detection threshold forces applied to unseen wire barriers by cautiously approaching human Ss.