What is the fine-grained topic of the following text: This magnetic lock is suitable for most doors and grips with a force of 600lb, which will make many would-be intruders step back (and look for a lift truck or other very heavy piece of industrial equipment because they'll need it to get through a door secured with this type of electro-magnetic lock). Only return the topic.
The strength and suitability of a magnetic lock for doors.