If I didn't love digital technology and respect the men and women who develop it, I wouldn't make my living writing about it. However, incidents like Tuesday's bizarre grounding of dozens of American Airlines flights due to an iPad app crash should serve as a reminder not to rely too heavily on technology.\nDigital devices are fallible. The code they run can become corrupt, connections to the Internet can be lost, and in some cases, outsiders can gain control.\nThe American Airlines mishap is a case in point. Today, American uses iPads as flight manuals instead of the huge volumes pilots used to carry. It's a good idea that saves lots of paper. However, the app is much more than a collection of documents. It's also used to distribute flight plans across American's fleet. Pilots need those plans, of course, so when the app crashed while they were on the runaway, they needed to return to the terminal.\u00a0 As a result, about 70 flights were temporarily grounded on Tuesday and passengers, particularly those who needed to connect to other flights, had to scramble to make other arrangements.\nFortunately, the result was merely inconvenience; no one was hurt, and there were no accidents, but a lack of a backup plan can also have serious consequences.\nA number of years ago, a young family from my neighborhood was traveling back home to California from the Pacific Northwest. While heading south on Interstate 5 they decided to take the far more scenic coastal route via Highway 1. Unfortunately, their GPS directed them to take a small, local road west to the coast.\u00a0The GPS's map didn't indicate that the road had been closed because of snow.\u00a0They got stuck, and the father, who had gone searching for help, died of exposure. Ironically, that man was a technology editor.\nOther travelers who trusted technology have also been misled. For example,\u00a0another man died in Death Valley\u00a0in 2011 after his GPS directed him to a old road that was no longer in existence.\nIn both of these sad cases, the fault wasn't with the devices, but with the data they used to suggest routes. If the GPS data is inaccurate or out of date, the directions will be useless.\nMore recently, companies have sold keyless locks that allow users to open the doors to their homes or cars using smartphone apps. That's convenient, but what happens when your phone runs out of power or the app just crashes and won't work? If you had the foresight to also install a standard lock, and remembered to carry your keys, it might not be a problem. If not, you're out of luck.\nBad guys already figured out ways to spoof these electronic locks. For example, a few of my neighbors tell me the electronic locks on their cars were apparently defeated by devices that scoop up and copy the low-power signals broadcast by the little fobs the people use to unlock them. One neighbor now keeps his electronic key in his freezer when he's at home so the signal is blocked.\nWhat will happen when people connect everything in their homes, from smoke alarms to ovens, to the Internet of Things? Will a software glitch turn on your connected oven while you're on vacation? If you have a connected camera inside your home, what happens if it gets hacked? A software failure in a driverless car tooling down the Interstate could give a whole new meaning to the phrase "software crash."\nI'm hardly a Luddite, and I'm not worried about a\u00a0robot apocalypse, but digital technology is fallible, and relying on it can be dangerous. In other words, when it comes to technology, always have a Plan B.