A tire pressure sensing device for a tow trailer that signals the driver of the tow vehicle subsequent to deflation of at least one tire mounted to the trailer. The tire pressure sensing device further includes a base plate mounted to the axle of the tow trailer releasably secured by a generally u-shaped clamp. A switch is superposed on the base plate. The switch further includes an actuating rod support member and an actuating rod extending in a downward direction. The actuating rod biases the switch to a closed position subsequent to deflation of the tire thereby electrically activating a warning indicator.