A while back, I reminded people that they should tip their Uber drivers. But a common response was essentially, “I’d like to tip, but half the point of Uber is not having to carry cash. And there’s no option in the app. So how do I do it?” Well, perhaps with Pax, a little seatback system made to do nothing but accept tips, cash or card.

There’s really not much to it; you’ve probably seen similar systems in some cabs that show ads and let you pay without the driver having to fuss with some decade-old system up front. It’s a custom Android build with a card reader and strong box with a slot for cash.

Since in an Uber you’d be paying automatically with the app, this would be strictly for the tip side of things: select an amount, swipe and you’re done. Pax is looking for $50,000 on Kickstarter to get this thing out in the wild.

Its creator, Azarias Reda, says that he originally made it just as a DIY project to help his uncle, who drives for Uber full time, earn a little extra cash. He said the prototype pulled in $10-20 per full day — not a lot, but it covers a shift meal and some gas, and that’s a whole lot better than nothing.

Of course, Lyft and other services allow tips right in the app, which is, I think everyone would agree, a better solution. But Uber is the most popular rideshare app and I wouldn’t bet on them allowing tips any time soon. It goes against the narrative the company has been cultivating for years.

So for Uber users, or for situations where perhaps one of several riders wants to throw a little extra down for a job well done, Pax could be a decent option — provided it works as advertised.

More than half the tips in a test run of the system in Washington, D.C. were on cards. The plan is to offer flat 3 percent fees on all transactions, and have the boxes operate essentially independently; no one will be taking a cut of your dollar except the driver and the payment processor.

Which payment processor that will be exactly is still up in the air, but either Square or PayPal should offer terms easy enough that 3 percent will be possible.

In the meantime, Pax is looking for the money to find out. Pax devices start at about a hundred bucks, though hopefully they’ll pay for themselves pretty quickly.

Featured Image: Pax