Such a long distance can only be reached by using RF/ID products (Radio Frequency Identification Devices). I do not think that there is a special sensor for that, but an RF interface can be found. Look at Symbol or Intermec websites.
I doubt if theres such a thing as a wireless prox switch, but why not just buy a normal prox and hook it up to a separate RF transmitter? 100m is definitely not a problem.
I can help you with this application if you want to contact me off list.
We have used non-visible laser sighting that works excellent. It will even give you a distance value if required. If you need us to help you engineer this further we can help you. Thanks.
We have developed a new product using magnetic (non-powered) prox switches with a wireless transmitter. The unit will transmitt the idenity of the prox switch along with its current status (open or closed) to a distance of 300 feet. The receiver is connected to a PC via a serial link using Com 1 or Com 2 at a baud rate of 19.2K. We are testing the system and it appears to be bullet proof.