The end of 3G is not just about phones

But as our ace tech columnist Hiawatha Bray warned in December, older cell phones aren’t the only victims of the 3G shutoff.

Millions of cars still on the road have 3G modems, which can be expensive to replace if the manufacturer even offers an upgrade. And what about all of the 3G modems connecting home security systems and medic alert necklaces? Some could stop working today if they haven’t been upgraded.

Andmy old Kindle e-reader’s free cellular connection? Gonzo. (I can upgrade to a new model with 4G cellular for $350.) Even the ankle bracelets people out on bail or parole must wear could be knocked out of commission, as Hiawatha reported.

So why shut down 3G networks and potentially anger so many customers?

The wireless carriers each have a limited amount of spectrum, the government-licensed airwaves they use to carry all our calls and data. Some of the best spectrum bands, with signals that travel the farthest, have been reserved for 3G. But with almost all users now on 4G and 5G tech, the 3G airwaves could be put to better use.

AT&T points out that it has been warning about today’s shutoff for three years, assisting consumers and some service providers as they transition to newer gear, and even put up $100 million in incentives to convince recalcitrant businesses to get on board and offer upgrades. (Alarm service ADT has been offering a free upgrade for its customers’ systems with a 4G module, for example.)

Not everything has been fixed, though. I took my brand new electric car with its modern cellular tech to Concord recently and plugged in at a parking lot charger. The device worked fine, but offered a warning: Its 3G connection needed to be upgraded.

Aaron Pressman can be reached at aaron.pressman@globe.com. Follow him on Twitter @ampressman.