A wireless temperature monitor probe includes a spike for insertion into an object for which a core temperature is to be monitored and a head at a proximal end of the spike. A sensor inductor coil is in the head and is used for wireless interrogation by an external detector unit to determine the core temperature. The spike axis is not in the plane of the inductor coil in the head, for example so that there is a bend between them. This makes it easier to insert the spike while maintaining a desired orientation of the head, in particular to enable correct communication with the remote detector unit. In addition, it enables the head to be positioned against the object so that the probe takes up a minimum amount of space.