Magnetic switch?

Certainly. Consider the sensors on magnetic mines. Think of the needle on a hiking compass. The question is not one of distance, but of the change in local field strength that can be created and detected. The more sensitive the switch, the more likely it is to respond to unintended inputs.

Jerry

I don't know about 12-6" away, but look into Hall Effect sensors.

Hope this helps,

Matt

Also look into "magnetic reed switch" and "magnetic proximity switch" or "magnetic prox switch".

'Sporky'

6" and especially 12" is kind of stretching it. Magnetically actuated switches work well in ranges up to 1".

However, it is possible to sense even smallest quatities of magnetism - squid sensors do it.

Also, in magnetic switching circuits there is always 'another side' - the magnet. need larger distance - use larger magnet. If the application can bare it of course.

Hall sensors are the crudest devices, magnetoresistive sensors offer higher sensitivity, but require some compensation techniques. Then there are flux gates.

The usual sourse of error limiting possible accuracy - manetic field of earth.

There is plenty application literature on Internet provided by manufacturers of magnetic sensors.