Welcome to the Official Guide to No Safety in Numbers. A biological bomb has just been discovered in the air ducts of a busy suburban mall. At first nobody knows if it's even life threatening, but then the entire complex is quarantined, people start getting sick, supplies start running low, and there's no way out. This is the ultimate guide to the book that started the series!
Electromagnets are used in things that have moving parts, eg. CD players, heads on Hard drives, automatic doors in a grocery store, electric windows, motors etc., Some examp â¦ les include: You can slide the bolts of locks and latches, tap out telegraphic dots and dashes, open and close switches in distant electric circuits.
Electromagnetic (EM) pest repelling devices claim to affect the nervous system of ants, spiders, mice and other rodents. Ultrasonic. Ultrasonic devices operate through emitting short wavelength, high frequency sound waves that are too high in pitch to be heard by the human ear (generally accepted to be frequencies greater than 20,000 Hz).