I am seeking to make a product that would need to trigger a mechanism only in reverse to how a proximity card works and with a power source no greater than a 9 volt battery, preferably smaller.
Same as a proximity card will trigger a mechanism to open a door, I seek the opposite, once the RFID leaves a distance of 3.5 feet away from the product a trigger will allow a spring activated lever to move a very short distance there by blocking a wheel. This as you might imagine is a safety device. . The trigger and spring load need to be easily reloaded by hand.
Compared to all the inventions in the world this is very very simple but will change the world a great deal and make it much safer. I am thankful for any help. I’ll never be able to do this on my own.
I don’t think you need a different device. You just need to reverse the interpretation of said device. If this is an RFID system. You could program the reader to check for a card/tag/chip every expected time frame. If there is no reply for X checks then disable the device. I could help more if I knew a bit more about your application.
Be careful and thorough with safety devices. You need to be aware of how the device operates in response to every possible situation. Not just what is expected. There are many cases where a safety device doesn’t work in a unique situation or works at cross purposes in an emergency and results in harm.
How is any different in concept and basic function from some car “keys” ? When in proximity to the car, the doors will unlock and you can start the car w/a push button. When the “key” gets some distance away from the car the doors lock and the alarm is turned on automagically.
Since this is a safety product, before you go any further, I suggest you make a table of all the things that can go wrong with this idea, how likely it is to happen and the impact each fault has.
Once you have that done, then ask yourself if the worst case failure is acceptable. Then you can make the decision whether to proceed or not, and what changes may be needed to make it safer.