Electromagnetic door holder

An electric current typically energizes the electromagnet to attract and hold the steel plate, keeping the door open.

On the other hand, security doors may close, latch, and lock, to prevent passage.

In life safety and security applications, electromagnetic door holders must be very reliable; the simplicity of the mechanisms helps considerably.

They are designed to be fail-safe in that anything interfering with their operation (such as a power failure) will cause them to release the doors and allow them to close.

[2] To overcome possible remanent magnetism, which could cause the electromagnet to fail to release, some door holders are equipped with a spring-loaded pin that helps push the magnetic plate away from the electromagnet when the power is cut.