With time and use microwave leakage often develops around door seals, hinges and the metal fittings of a microwave oven. Such microwave energy is capable of penetrating living tissue to a depth of approximately 1.18". For this reason microwave oven manuals often recommend periodic checks of seal integrity. This detector is designed for this purpose and will determine on a pass/fail basis whether the microwave oven is safe or should be returned to an authorized dealer for repair. Since microwave ovens should not be operated empty a beaker for water is included along with full instructions. No batteries are required as the detector is powered by the microwaves themselves. Magnetic back for attachment to the oven. 4 3/4" x 2 1/8" x 1 3/4".