A fused refractory product having the following average chemical composition, in % by weight on the basis of oxides and for a total of 100%: ZrO2: 30-50%; SiO2: 8-16%; Al2O3: balance to 100%; Y2O3\u226750ZrO2 and Y2O3\u22665%; Na2O+K2O+B2O3\u22670. The present invention can effectively realize the N+M backup for the base band processing module by adding a switch unit, therefore solving the technical problem of complexity and high cost for wiring and interfacing when having a large number of BBP and TRX modules. In another embodiment, a relative signal strength indicator -based process is used to determine the RSSI of packets received at the first transceiver from the second transceiver for adjusting the packet transmission rate. A user may also add the opening by merely drilling an aperture or slot, sized appropriately for the corresponding hook on the security device.