The best protection is your health and a feeling of belonging and safety. Resting on your inner self without fear is the best remedy against outside influences.
Having said that, it remains a fact that some people are more susceptible than others to the influences of their environment.
If something is not right, it is always imperative and preferable to address the cause of the problem. Placing a crystal on a health hazard does not make it harmless. In fact, we know very little about the amplifying powers of crystals; they can make things worse, too.
Once the problem (e.g. electro-pollution) has been addressed, harmonisers and energisers may be helpful to stabilise health and wellbeing.