When surgeons remove a malignant tumor, they have to be sure to get all the cancer cells and determine whether the tumor has already sent micrometastases into the neighboring lymph nodes. EPFL, in partnership with the University Hospital of Lausanne (CHUV), has developed two compact, light, and wireless probes that help doctors with both of these tasks. The Gamma probe improves on similar devices already in use in radio-guided surgery, and the Beta probe is a new type of device able to detect extremely small bits of cancerous tissue. The two probes, measuring 20 centimeters long and weighing 100 grams, are easy to work with and to insert into the surgical wound. The probes guide the surgeon with auditory signals similar to those of a Geiger counter, accurately locating what the human eye often cannot see.