Designing a Small Standalone Proximity Reader for 10 Key Fobs With Dry Contact Output

I have an alarm type product that I have installed in a few small retail stores. It gets shunted by being triggered by ANY dry contact. (2 wires). I have used keypads, key switches, card readers, even just rocker switches. I am trying to get someone to design a very small proximity reader that will read approx. 10 key fobs and give me a dry contact out. No information to a computer or panel. Basically, a "dummy reader". Anyone have any idea where I start?

Thanks in advance,

Jeff

I'm wondering if it might be easier and even less expensive to buy the key fobs and reader already built. Googling key fob and reader brings up several companies. And Amazon.com and Ebay have these devices.