A lifting device sensor unit comprises a housing, a first global navigation satellite system receiver, and a wireless transceiver. The base station has a BS-spread-spectrum transmitter and a BS-spread-spectrum receiver. One or more events associated with the creation of a message are monitored. Retention structure on the work tool is configured to prevent removal of the work tool from the housing when the tool retention member is engaged with the housing. Adjustment screws on the vertical plate or locating arms urge planar pads on the vertical plate against the rear wall of the receiver plate against the rear wall of the receiver to firmly mount the rear sight device on the receiver. After obtaining the private decryption key from the key generator 120, the receiver 110 uses it together with the element rP and the bilinear map to compute the secret message key gIDr, which is then used to decrypt V and recover the original message M.