We present a new, handheld probe for radiotracer detection in vivo and inside operating theatres, where PET scanners cannot be used for radioguided surgery. The device is based on scintillation detectors optically coupled to Silicon Photomultipliers (SiPMs). It is wirelessly connected to a PC, which, among other functions, optimises operating voltages to compensate for changes of the detector temperature. The probe is primarily aimed at and optimised for direct detection of beta(+) radiation at short distances. Nevertheless, it is also sensitive to gamma, thus enabling the surgeon to localise tumours roughly at larger distances. The use of the probe has been demonstrated in first preclinical pilot trials with oncologic patients at the CHUV university hospital.