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Jan Cocatre-Zilgien shows you how to make a skin temperature transmitting device in the latest Citizen Scientist -

Any parent who has had to take care of a feverish child at home knows what a source of emotional stress and anguish it can be. This is magnified at night, as fever often tends to get higher then. Unchecked fever may create complications of its own, such as dehydration and febrile convulsions in infants. The lack of sleep resulting from periodically monitoring the child can be very tiring for the parents, especially if the fever spans several days.

When small single-chip transmitter and receiver modules became publicly available, it was an invitation to design a skin temperature telemetry system for those parents. I used the very robust modules from Linx Technologies, with 418 MHz chosen over 315 MHz because of the slightly shorter antenna. Essentially, if the transmitted child skin temperature gets too hot (fever peak) or too low (malfunction), an alarm is triggered at the receiver. The version whose receiver is integrated with an alarm clock was patented in the USA under patent number 5,844,862, which shows variants and other complementary information. Figure 1 is a sketch of the completed device.