You will need quite a bit of money (Score 1)

I will have to disagree this is solely a human problem. Technology can solve this. But it is not cheap. It is claimed that a better to give a rough location rather than to triangulate, which requires a subsequent mapping. Details can be found in K. K. Yap, V. Srinivasan, and M. Motani, MAX: Human-Centric Search of the Physical World, Proceedings of ACM Sensys 2005, San Diego, CA, USA, November 2005. Available at http://wine.dnsalias.org/motani/publications.php But the cost is quite forbiddingly now. I actually have a working prototype but it is nowhere near economical. Good luck and let me know if you can find passive cheap readers with the range needed (about 1m). Disclaimer: I authored this paper.