If you are a Pokémon Go fan — or have an app-happy son or daughter — beware of the looming Data Apocalypse.

"The app may be free, but going over your data plan could cost you big time," says Jen Barrett, chief education officer at investment site Acorns and editor of the digital magazine Grow.

Only available since July 6, Pokémon Go has topped 15 million downloads, with users hunting characters like Pikachu, Charizard and Squirtle for an average of more than a half-hour every day.

For wireless companies, the Pokémon Go craze is perhaps the best gift they ever received. As T-Mobile CEO John Legere tweeted giddily to CNBC's Jim Cramer: "Since last Friday, # of active players doubled & their data usage more than quadrupled!"

The powerful data-suck stands to reason: Since the game uses GPS to continually track and transmit your location, and has you constantly on the move — where you might not have your normal network access — it is all too easy to chew through your data plan.

Here are some tips on enjoying Pokémon Go without having to upgrade your data plan:

1. Networking is key. Whether you are wandering through a Starbucks franchise or an airport or a municipal park with Wi-Fi access, make sure your smartphone's settings are automatically logging on to known networks, suggests Chuck Hamby, Verizon's executive director of corporate communications. The less time you play via a cellular connection, the better.

2. Close down unused apps. To be fair, it may not just be Pokémon Go to blame for rampant data usage. If you have a handful of other apps open at the same time, those vampires may also be sucking greedily at your data plan.

Notes Hamby: "Many open apps, especially those that provide location services, will continue sending and receiving data even when your phone or tablet is locked."

3. Moderation, moderation, moderation. According to the Pokémon Go Database (pokemongodb.net), users might expect to churn through 2-8 megabytes or more of data per hour, depending on the different types of play involved. Get too swept up, and that is when you could see the extra charges piling up.

"If Pokémon Go is played for more than six hours per day, an upgraded data plan may be needed," according to the site.

4. Beware of in-app purchases. Data usage is one thing, but in-app purchases can make it a pricey double whammy.

"If you are playing Po-Go instead of going to see a movie or paying for some other type of entertainment, it may be an even swap," says Barrett. "But keep track of what you're spending in real money on PokeCoins. It can add up quickly."

U.S. players are already spending a reported $1.6 million a day on in-app transactions.

5. Disable notifications. A secret culprit gobbling up data usage: E-mail and push notifications from various apps, which you probably do not pay attention to anyway.

Automatic app updates are not helping, either. Dig into your smartphone's settings and turn them off.

6. Make the kids pay. One sure way to make sure your kids have some skin in the game: Charge them for any data overages related to their playing. Otherwise, they do not have much incentive to curtail their gaming.

Chris Taylor writes for Reuters.