Digital thermometer with a probe/sensor on a 100cm cable and can be mounted with a suction cup.
Digital thermometers are ideal for keepers that heat a whole room or cabinet. When heating a large space with a heater you get a thermal gradient as you move away from the heater. With Cabinets, rack and shelf systems the higher levels also tend to be warmer as the heat rises.
In our spider rooms we place several digital thermometer in different locations/ heights so we can find the ideal location depending on the species. Cooler south American species are usually on the lower levels and warmer tropical species are either higher up or closer to the heat source.