Summer is for family vacations, share houses at the beach and theme park outings with friends. But how to keep track of a big group of travelers without a flurry of texts and calls? Are the children at the pool or the arcade? Who is already on the beach? Is everyone en route to the Ferris wheel or the Tilt-a-Whirl?

It’s easier than ever to find out, thanks to the proliferation of GPS-enabled smartphones and a steady stream of free or affordably priced apps. The number of active users of “family locator services” (smartphones with GPS and personal location devices) in North America and Europe is expected to reach 70 million in 2016 — up from 16 million in 2011 — according to a new report from Berg Insight, a research firm based in Sweden.

Certainly, you can keep tabs on fellow travelers using other methods, including cellphone programs like AT&T’s FamilyMap and Verizon’s Family Locator that let you keep a distant eye on family members, and tracking devices like the battery-powered GPS Atlas F100 and the Toddler Tag Child Locator, which uses radio frequency technology (your child gets a tag; you get a key chain transmitter). The good old walkie-talkie deserves an honorable mention (useful in places with spotty cell service like the backcountry or cruise ships). And, while it’s not a tracking solution, I’ll give a nod to Safety Tat customizable temporary tattoos: child-friendly graphics (dinosaurs, butterflies) alongside the phone number of your choice and the words “If lost, please call.” (It’s also a great gift for adults with existential anxiety.)

That said, tracking apps give you the most bang for your buck. You can locate your brood on a map without ever making a call, receive alerts if the kids venture beyond a designated area and turn your smartphone into a newfangled walkie-talkie. Below is a guide to the apps that can keep you together, even when you’re apart.

Virtual tracking

Family Tracker: The latest version of this app runs in the background of your phone, tracking any iPhone, iPad or Android phone on which it is installed based on its GPS location. You add people you want to track, and if they accept, you can then see their whereabouts on the app or the app’s website. Cost: $4.99; a “lite” version of the app with fewer features is free.

Find My Friends: You begin using this app for iPhone, iPod Touch and iPad by sending friends and family members a request to see their location. If they accept, you will be able to see them on a map. Remember: Unless you tweak your settings, they will also be able to see you. Cost: free.

Find My Kids — Footprints: This app for iPhone, iPod Touch and iPad tracks friends and family members who have also installed the app. There are two ways to track one another: by “significant location changes” (every quarter-mile to two miles as your phone detects new cell towers) or by GPS, which updates every 5 to 10 minutes (and drains your phone’s battery power). The app will also allow you to create “Geofences,” or areas, like the hotel pool, that you don’t want your kids to cross. And if they do? You’re notified. Cost: $1.99 for a three-month subscription; $3.99 for a year; $5.99 for two years.

GPS Tracking Pro: You can use this Android phone app to track friends and family in your neighborhood in real time. Each friend is represented by a thumbnail photo in his or her exact location on a map, enabling you to watch as they flit from one place to the next. Cost: free.

Smartphone walkie-talkies

iPTT push-to-talk: This app for iPhone, iPod Touch and iPad allows groups of people to chat live. It feels more complicated than it needs to be thanks to multiple channels, but once you get the hang of it, all you need to do is push the “talk” button and begin chatting. Cost: free.

Voxer Walkie-Talkie PTT: This app for iPhone, iPod Touch, iPad and Android is one of the easiest to use, allowing you to send live audio to friends and family and listen to their voices in real time. It’s simple to chat as a group, so it’s perfect for entourages. Just push the “hold and talk” bar at the bottom of the screen while you gab. Release when done. Cost: free.

Zello: This straightforward app is among the most reminiscent of walkie-talkies. Invite friends to be your contacts, then press a big round button with your thumb. Wait for the beep. Next, press and hold the button while you speak. Let go to hear the voice on the other end of the phone. Cost: free.

Monitoring the kids

Life360: This app uses GPS tracking technology that enables family members to see one another’s whereabouts on an invitation-only map, find lost or stolen phones and even see recent crimes in the area. When family members reach their destinations, they can let one another know by checking in with the push of a single button. If there’s a problem, they can push a “panic” button to send out a voice, email or text alert to family members. Cost: free.

MamaBear Child Tracking: This app for iPhone, iPod Touch, iPad and Android phones might as well have been named Big Brother. It allows parents to see the locations of their young ones on a map, receive alerts if they go somewhere off limits, learn when they make new friends on Facebook and, if they are teenagers, discover when they drive faster than Mom and Dad allow. Cost: free.