I have the new smaller plastic Sunpass. (Not the sticker) and used heavy duty velcro to attach it to the top part of my saddle bag just as you would with the suction cup to the windshield. Works just fine there. I know people that keep them in their pocket or put them in a pouch mounted on the bike as well. Its RFID so its pretty strong signal. As long as your bike is registered with that transponder and if you don't get picked up by a toll booth for some reason they will read your license plate and charge you that way. With the older transponder that is what happened. Didn't work quite as well and sometimes it would look like I ran a toll. Still showed up as paid on my account though. All good, just register it to the bike.

 

You can return that one and just register multiple vehicles under one transponder.

 

SunPass is in the process of phasing out the older style at no charge
for the new style.

 

I mounted the small one on the bike. I used the heavy duty (plastic) velcro and mounted it inside the right saddle bag cover. It works just fine. It gets picked up around 90% of the time. I just put the bigger one in my wife's car and left it there.