An electronic price tag, an electronic price tag system, and a method of updating an electronic price tag. The electronic price tag includes a reed switch sensor and a processor. The reed switch sensor is configured to sense a magnetic field adjacent to the electronic price tag to generate an output signal. The processor is configured to: receive the output signal of the reed switch sensor, convert the output signal into information indicating whether the electronic price tag is normal, and send the information indicating whether the electronic price tag is normal.