I have a portable Sun Pass which I take with me and use in rental cars. How do I know if it is transmitting? There is no way to check it out. How does it signal the camera when passing through the toll lane? All you know the costs of not paying for the rental car option of prepaying toll at rental counter. Thank you very much for any comments.

I am unsure which transponder you have (there are several models)....the model I have beeps with a green light when the toll is paid (it is battery powered). You can also go online and see the tolls that have been paid (after login)....

https://www.sunpass.com/index

More rental care information:

SunPass Customers:
SunPass customers using a rental vehicle may have their tolls applied to their SunPass account. Customers with SunPass Portable transponders may use their transponders in their rental vehicles. (It is strongly recommended that SunPass customers access their online SunPass accounts or contact the SunPass Customer Service Center to add the rental vehicle subscription to their account for the rental period.) Please remember to remove your transponder upon return of the vehicle.
SunPass customers that do not have their transponders in the vehicle are subject to the tolls, fees and charges set forth below and in their rental agreements.

SunPass Customer Service Center: 1-888-TOLL-FLA (1-888-865-5352)

be sure you have more than the minimum amount needed in your account - i park at mco and my sunpass let me in but when i tried to exit the next day i was denied. when i called sunpass they said i had gone below what it cost to park. turns out i did have enough in the account because they added to it when i hit my minimum, but it was below what i needed when they looked. they only look when you enter to see if you have the funds to exit. and they added funds from my credit card after that

now i keep it funded at a much higher minimum - although now i do not use the sunpass for parking. it took forever for me to get out because i did not have a ticket and by the time they verified my entry time i could have been half way home

but driving toll roads in florida without a sunpass is not a good idea - many exits do not have a toll collector - you need exact amounts.

And Dade county doesn't accept cash at all.