Abstract: A low tire pressure sensor for use in detecting deflation of a tire while it is supporting a tow trailer from a surface as it moves in a given direction therealong. The sensor comprises a sealed housing holding a pivot shaft and enclosing an electrical contact switch which is activatable upon rotation of the pivot shaft from a first biased position to a second position. The pivot shaft has an outside portion which extends sealingly and rotatably through a portion of the housing. A resilient sensor rod is mounted on the outside portion of the pivot shaft and extends therefrom at an angle forward in the direction of movement of the tire when the pivot shaft is in a first biased position. The resilient sensor rod has an end spaced a predetermined distance from the surface, such that upon at least partial deflation of the tire, the resilient sensor rod contacts the surface and is moved over center to rotate the pivot shaft to a second switch position, at which the electrical contact switch is activated.