Answer:
EMF radiations
Step-by-step explanation:
Electric and magnetic fields (EMFs) radiation is a terms collectively used for invisible energy waves governed by electricity and magnetic forces. These radiations are usually produced when some thing is operated by use of electrical power.
In watches , mercury or other ionizing battery cells are used to power the watch and hence it can be stated that EMF radiation are most useful to investigate.
Some time high frequency waves such as ultraviolet rays and X-rays are considered as form of EMF waves