Beag, I wish you brought this up at NEXXT..... I have the setup with an 8500. I love the 8500, and the HARD system is awesome.
Not sure about battery life. I had it sitting around since March, and finally got to hooking it up right before NEXXT. I'm guessing I have @ 20 hours on the batteries so far. If I recall, it takes a pair of the CR2032.
I don't think the signal is strong enough for another rider to pick up. If you have power to the transmitter, but have not turned on the detector, it sends a constant flash. I just tested it and it seemed to get intermittent as I got about 10 or 15 feet away from the bike and moved around. I asked when I purchased, and he will sell extra receivers to mount in spare helmets.
I paid $140 for the HARD during Daytona bike week, direct from Aaron of LegalSpeeding. It's $160 on the web site now.
http://www.legalspeeding.com/product.htm
I got the Escort 8500 here
http://www.sbhcorp.com for $260 w/free shipping last year. You have to call for current price. They don't post on the web. 800-451-5851
If you get the 8500, be sure to buy a plain power cord, that does not have the smart cord feature, so you can hardwire it. The cig. lighter plug that comes with the unit is a smart cord.
Steve