The ornamental design for a wireless barbecuethermometer, as shown and described.
FIG. 1 is a front elevation view of a barbecue thermometer;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof,
FIG. 5 is a top plan the view thereof;
FIG. 6 is a bottom plan the view thereof;
FIG. 7 is a first perspective view thereof; and,
FIG. 8 is a second perspective view thereof, shown in an open position.
The broken lines shown in the drawings depict portions of the barbecue thermometer in which the design is embodied that form no part of the claimed design.