As has been said before, you can go from as simple as your phone to several thousand dollars invested in recording gear.
If I want to make a quality sounding recording or a video, I have gear that will do it quite well. It's always set up and ready to go, but it still requires some effort and is way overkill for just catching a practice session.
When I just want to capture a lick so I don't forget it tomorrow or simply hear something back that is otherwise not for (other) human consumption, I have a Zoom H1 audio recorder on my desk. All I have to do with it is turn it on and press record. To listen to it, I can either use the built-in tinny speaker or plug a set of earbuds into it. If its something worth keeping I can plug the H1 into a USB cable and download it to my computer.
The H1 I have is no longer made, but Zoom now has the H1n, which adds some nice touches that make using it more simple than the original H1. Depending on where you shop, it's about a hundred bucks. You will also need to buy a SDHC micro memory card for it. It will take up to a 32 gigabyte card, but unless you're using it to archive audio, a smaller card will do quite nicely.
You can get an equivalent unit with video record capabilities for about $50 more in the Zoom Q2n recorder. The audio quality is on par with the H1n.
@MikeR has one that he has used to record previous BGU Live events (I believe most all of the 2017 videos for BGU Live were recorded on it). You can check out the audio and video quality of it here:
https://bluesguitarunleashed.com/forum/index.php?threads/bgu-live-videos-photos.19430/#post-276582