Some Philadelphians traveling outside the region by bus or train have noticed an unexpected perk of having a SEPTA Key Card in their wallets: free rides elsewhere.

SEPTA has confirmed reports on social media of visitors to Chicago and London getting on those cities’ transit networks using their SEPTA Key Cards.

“A customer with a Key Card who taps it on the systems in Chicago and London (possibly others, but these are the two that we’ve also heard about) will have the fare paid/validated for just their first ride from the MasterCard/GPR [prepaid debit] side, even if they don’t have a GPR balance,” SEPTA spokesman Andrew Busch said in an email.

SEPTA Key Cards have a prepaid debit function — separate from the “travel wallet” that holds passes and money just for fares — through a partnership with MasterCard. Key holders must actively set up the prepaid debit accounts by specifically adding funds to them before they can be used. SEPTA recently activated that function, but few riders have used it.

One Philadelphia resident, who asked not to be named for this article, noted that his Key Card scanned on London’s Underground on a recent visit. Even though he managed to get on the Tube with his Key, he didn’t get charged.

“I’m looking at the balance after each trip, and it looks like it didn’t record the trip at all,” he said. “I never set up a [prepaid debit] account. So maybe Transport for London got stiffed?”

If anyone got stiffed on the ride, it’s MasterCard, Busch said in the email.

“This is a MasterCard function, and from what we understand, the transit agencies do receive the fare, but how exactly that happens on the back end, I’m not sure. The funds definitely do not come out of the travel wwallet,” Busch wrote. “After that first ride, the Key Card/MasterCard would be declined unless the cardholder adds GPR funds to their account.”

Riders have reported similar success unlocking access to Chicago’s CTA by tapping their SEPTA Keys against that system’s fare-card readers.

Transport for London was one of the first transit agencies to adopt contactless fare cards with its Oyster cards in 2003. The Chicago Transit Authority followed suit in 2013 with its Ventra card — a glitch-filled, seemingly rushed rollout that inspired SEPTA’s slow, piecemeal implementation of the Key. Both those systems were built by Cubic; SEPTA contracted with Conduent (formerly ACS Transport Solutions).

Neither Transport for London nor CTA responded to PlanPhilly’s requests for comment.