Once you've download a map area that area will simply be available, even when your phone is out of range or in airplane mode. You don't need to do anything special, just use the app as if you had service. You will see a box indicating the map areas that you've successfully downloaded. To delete downloaded maps from your phone, go to Settings and then tap on Map Downloads. From here you can manage your downloaded maps. 

Any tips for extending my phone's battery?

  • Turn off wifi and bluetooth. You're unlikely to use these in the backcountry. You may also consider putting your phone in airplane mode.  

  • Consider carrying a small battery pack. We do, especially on multi-day trips.

  • Turn off your phone at night. Many people use their phone to take photos during the day. But there's not much reason to keep your phone on at night. 

  • Keep your phone warm. A cold phone uses more battery. Who knew? 

  • Turn on Data Saver mode (Android). Turn on Data Saver mode, but make an exception for Cairn. This offers battery savings without interfering with GPS functionality and location tracking for Cairn. To do this, go to your Android Settings app, choose Data usage, choose Data saver, then Allow app while Data saver on and then toggle on Cairn.

  • Put your phone into low battery mode (iOS). This offers significant battery savings without interfering with GPS functionality and location tracking. To do this, go to your iPhone Settings app, choose Battery, then turn on Low Power Mode (or just ask Siri!).

How do I add my own destination to the app? 

Tap and hold anywhere on the map to drop your own custom pin. If it’s on a trail, you’ll be able to get all kinds of interesting information about that spot. 

How does the free trial work?

Currently we automatically offer a 30-day free trial of our premium features.

On iOS: Upon your first use of the app you are automatically enrolled in our free trial period. At the end of those 30 days there is no need to cancel anything; simply sign up for Premium membership if you'd like to continue using those features,

On Android: The free 30-day trial is only offered when you first attempt to use one of the Cairn Premium features. If you choose to enroll in the free trial you must cancel before that time period is up if you do not wish to be charged.

Premium features include:

  • Sharing of your real-time location with your safety contacts

  • Automatic overdue alerts

  • Downloaded maps from anywhere in the world for offline use

If you do subscribe, you can cancel your premium membership through your phone's Settings app (iOS) or Google Play app (Android). You can always see cell coverage on maps and view trail info such as distance, elevation, and estimated time of arrival, regardless of your subscription status. On iOS, you can also record and save your track.

What is the difference between the blue and gray dots?

Blue dots indicate a spot cell coverage was detected by Cairn users. Gray dots indicate that no coverage was found. Tap on the dot to see which carrier(s) did or didn't have coverage at that spot.   

Will Cairn work if I lose cell reception?

Yes! It is designed to work offline, but it really helps if you download the map for the area you'll be exploring before you lose reception. We recommend doing this at home over wifi. Our safety notification feature only works if you set it up before you're out of range. But rest easy knowing that your safety contacts will be alerted if you're overdue regardless of your phone's status.  


Yes, you can tap on a point to see which carriers have coverage (or not) at that point. We don't have data for every carrier (or every point, for that matter) as this data is crowdsourced by other adventurers who use Cairn. 

Can I make emergency calls via other carriers?

Yes! You may be able to make an emergency call (to 911, for example) even if your carrier doesn't have coverage. Your phone just needs to operate on the same frequency band as a carrier that does have coverage. Always try to call 911 in an emergency, even if it doesn't look like you'll get through.


Once you've started a Cairn, your contacts will have a link to a map that will show your progress. If you are using an iPhone, you will see an I'm OK button that makes it easy to send all your emergency contacts a message along with a map of your current location. Choose from one of our pre-filled messages (e.g. Made it to the top!). or write your own. If you don't have coverage (and this is the best part), the app will send your message/location as soon as it notices that you have coverage again. We think it's a pretty handy feature. Once you end your Cairn, we let your contacts know you're safe.


We're happy to report that (on iOS only) after you send a notification to your contacts, you'll see the points of cell coverage that you've collected. It's a nice way to see your own trail without using your phone's GPS constantly. You can also track your stats, which also shows you distance covered, elevation gain/loss and an estimated time of arrival (ETA).

What happens when I put my phone in airplane mode?

Unfortunately, for iOS devices, we can't tell the difference between airplane mode and no service. So any data you iPhone users collect when in airplane mode will be recorded as no coverage. Android folks, your phones give us a little more information. However, we know that using airplane mode in the backcountry saves your battery. And so we take this into account in our coverage aggregation algorithm for an area. Please use airplane mode as you normally would, but if you have an iPhone, know that it will be recorded as no coverage.


Absolutely. And the rest of the ten essentials as well! Cairn is just another tool to throw in your cache of safety gear. We are not advocating that you use your phone at every opportunity, and we get that you probably want some peace and quiet when you're out. But the vast majority of modern day wilderness rescue operations are initiated by cell phones. We'll know Cairn is a success when it helps save a life.  


Phone batteries don't like the cold and your phone will shut itself off even if it still has charge. Some people keep their phones in their inside jacket pockets, or slip in a hand-warmer to keep their phone batteries warm.

HOW can i help gather more data for the coverage map of the wilderness?

The best way is to get more people using Cairn. You can invite people via Twitter or Facebook using our handy links. If you're a member of a Facebook or Yahoo outdoor group, share this website there. We can use all the help spreading the word that we can get. 

My question isn’t answered here. Now What?

Please email us at adventure@cairnme.com. We’re anxious to help.