The transponder has different colored lights. One of the lights will warn you when funds are low. These lights are actually at one of the booths in the cash lanes, not on the transponder. I've never bothered to try to find them. I suppose that it'd do no good to have them in the open road tolling lanes. You'd never see them at 70 mph. At any rate, I-PASS works great, and I highly recommend it, even for very occasional tollway users. Because it was only an additional $10 (refundable deposit), I picked up a second transponder for the second car. For me, that's easier than remembering to move the transponder. It wouldn't have been necessary, though. If you forget your transponder, the system will photograph your license plate and match it up to your account. There won't be any penalties, and you'll still get the discounted rates. The only difference will be that if you log in, the "video tolls" won't show up immediately. As mentioned earlier, changes to your account happen within 15 minutes. When you go online, you can make a payment, add or remove vehicles, add transponders, and change your automatic replenishment amount. The only thing you can't do is change your low balance threshold, which by default is $10. You can do that over the phone. In theory, if you're automatically replenishing and your credit card is up to date, you shouldn't have to make any payments manually. If you somehow manage to "overdraft," you have seven days to deal with it. In the meantime, you won't be penalized, and your tolls will still be discounted. Overdrafts shouldn't happen under normal circumstances, though. If I were to anticipate heavy use, such as a trip that covers several E-ZPass states, I might consider a manual payment just to be sure I'm covered in case of any glitches. While that shouldn't be necessary, posts here indicate that E-ZPass isn't quite as user-friendly as I-PASS. Not every state offers discounts. On the Chicago Skyway, you'll pay the full toll. Plus you'll pay a 3 cent surcharge for using Illinois' system rather than Indiana's. The rest of Indiana might be discounted; I don't recall. But you'll be hit up for three cents for using I-PASS. That still beats stopping and messing around with cash. One other tidbit… if you happen to be carrying more than one transponder in your vehicle, wrap any extras in aluminum foil to keep them from registering at the tollbooths. If you pick up extra transponders in person, they'll do that for you.