Book anti-theft magnetic strips, also known as EM anti-theft magnetic strips, are anti-theft devices made of metals such as cobalt, nickel, and iron. They are formed into an amorphous structure through a high-temperature melt-spraying process, resulting in high magnetic permeability, and are primarily used in the field of book anti-theft.

The magnetic strips are divided into two types: iron-based and cobalt-based. Iron-based strips are cheaper but more susceptible to stress, which can lead to a decrease in sensitivity, while cobalt-based strips are more stable. The working principle is based on the magnetic strip being periodically magnetized in a low-frequency alternating magnetic field. The high permeability generates harmonic signals that trigger the alarm.

The detection system generates an alternating magnetic field through a transmitting antenna, and triggers an alarm mechanism after the receiving antenna captures the harmonic signal of the magnetic strip.