A good friend of ours (another MSF RiderCoach and factory demo rider) was on a cross-country trip last year when he had a catastrophic blow-out of his front tire while on the interstate at 70 mph. After all the crashing and carnage had come to a stop, he found himself lying in the median strip, some distance from his bike. He was conscious but unsure of his physical condition. Fortunately he had his SPOT on his person, rather than attached to the bike. He was able to reach the SPOT without significant bodily movement and activate the distress beacon. Help arrived almost immediately. He was transported to a local hospital and kept overnight for observation, then managed to walk out the next day. (Something to be said for good, full protective gear here, as well...).
The point of this is that if the SPOT had been on the bike, he would have been forced to move to it to call for help. In a worst case scenario, he might not have been able to reach the SPOT at all. This taught me an immediate lesson, as I used to carry my SPOT on the bike. Now I carry it on my person.
So, where do you carry your SPOT?