Not too nightmarish of a nightmare, thankfully. I had gone to a remote part of the California coast with my brother, sister, husband, and baby, with our car and a Zipcar. One morning, after waving the card over the reader what felt like a thousand times, we realized the thing was no longer working. We used a landline to call Zipcar, whose representatives told us about the reception issue. We could abandon the car, they said, and they would waive the normal fee. (Thanks!) Or we could wait for a tow. Unable to get a cab to come to us, we waited. A tow truck took us to a lot with reception, where the rental failed to start. We needed another tow to a town where we at last abandoned the Zipcar and made our way home.

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It all worked out fine. But it might not have. I shudder to think about limping back to a trailhead with no more water in my backpack, only to find a car that would not start. Or getting locked out and marooned in Death Valley, perhaps with medicine trapped in the car.

The “out-of-comms scenario when a member is unable to access a vehicle is extremely rare,” Jeff Prus, Zipcar’s vice president of product and experience, told me in an interview. But it does occur. Zipcars in general work just fine when they do not have cell service, he said, as they have some internal memory that lets them function even when out of touch with the company servers. Indeed, making sure that the cars work when out of reception is a “mission-critical success factor” for the company, he said. Still, cars without reception become vulnerable in a few scenarios: when members lose or do not have their physical Zipcard with them, when they exceed their reservation time or want to extend their Zipcar reservation, or when the vehicle battery dies. That last scenario was the one my family and I found ourselves in, though we did not know it at the time.

Such issues might be rare—Prus declined to give any hard numbers to quantify how rare—but online, tales of the dreaded “out-of-comms scenario” abound. Zipcars abandoned for days; Zipcars stuck in the woods; Zipcars stuck on the seashore; Zipcars stuck in garages; Zipcar users resorting to hitchhiking.

Tess Rinearson had finished a 17-mile hike to the top of Mount Tamalpais with her boyfriend and some friends, only to return to a Zipcar that would not start. “We were super wiped,” the Bay Area technologist told me. “We tried tethering. We tried walking to get service. We realized it’s not us who need service. It’s the car that needs service.” They ended up using the Wi-Fi at a fire station while Zipcar sent them a tow truck from the East Bay. “We actually got really into figuring out what was going on,” she said. “Everyone on this hike was a programmer. We were like: How is this failing?”