There are all kinds of reasons why you might want to set up a dash cam in your car: Everything from settling insurance claims to capturing footage of passing meteorites. And if you're taking your smartphone along for the ride anyway, then you may as well get it to take over dash cam duties too.
What you need
Assuming you've got your hands on a suitable phone, your next port of call should be a mount to keep it in place while you're motoring around -- you might already have one if you use your handset as a sat nav. Obviously it needs to be one that leaves the rear camera free.
Thanks to the heavy lifting required to keep your camera on and recording all the time, it's a good idea to get a mount that charges your phone too or pick up a separate cable to do the same job. With your kit in place you're ready to find a dash cam app for your handset.
Picking an app
There are quite a few apps out there ready to meet your dash cam needs. The selection is more limited on iOS, where Car Camera and CamOnRoad seem to be the best of the bunch. The latter is free and the former has a Lite version available if you want to test it out before you buy.
CamOnRoad is also available on Android, along with DailyRoads Voyager, AutoGuard Dash Cam and CaroO, the last of which can also monitor your car's vital statistics at the same time. All of these are free (or have free versions) so you can see which one suits your device best.
You should double-check the laws of your own land as well before you get started: Here we've tested CamOnRoad and DailyRoads Voyager, as they can work in the background behind a sat nav app (or any other app) -- in the UK it's currently illegal to drive a car with a live camera feed in your field of vision.
On the road
It's important to familiarise yourself with the various controls and options of your chosen app before you hit the road, as you don't want to be fiddling around with buttons and sliders on the Interstate. Start the record process and you're ready to get out on the road.
Most apps let you set a specific amount of storage space and the recorded video then loops around using that block of memory -- it means you'll have to remember to stop recording if you want to keep something. DailyRoads Voyager has a specific Retain button for saving recent footage, which stays visible on top of whatever app you have open (like Google Maps).
CamOnRoad offers up some useful augmented reality features too: You can see various points of interest as you drive around, such as nearby gas stations and even speed cameras. Speed, distance and time are all recorded, and there's an optional cloud storage service for your clips.
Of the two apps we tried, CamOnRoad offered the most appealing interface and more features, but DailyRoads Voyager offered simpler operation and better integration with other apps, so it's worth testing out a couple of different ones to see which gives you the features you need.