A versatile label holder adapted to be stably secured in C-channels of various widths such as are found in Lozier, Madix and Streater shelves without significantly modifying the angle normally presented with each of these shelves. A heater of the core temperature sensor heats a peripheral area to a temperature greater than the core temperature. In one embodiment, two devices communicate with each other through the one-wire bus. In the memory field a mean signal curve for the time interval of one second is generated over a period of several seconds.