Example aspects of a nozzle cap for a fire hydrant and a method of detecting a leak in a fluid system are disclosed. The nozzle cap for a fire hydrant can include an outer housing defining a first end, a second end opposite the first end, and a substantially circumferential wall extending from the first end to the second end; an antenna coupled to the substantially circumferential wall of the outer housing; a cap cover coupled to the outer housing at the first end; and an inner housing coupled to the outer housing at the second end.