This came about when I wanted to bring my phone to the beach but not wear a belt pouch. It's not waterproof but I just wrap the phone in a plastic bag and put it inside. This is also great for jogging or other sports. It'll hold a music player, phone, keys, wallet, etc. Just make sure you buy (or make) a pouch big enough for your needs.
The reason I made this is that I couldn't find anything specific for what I wanted to do. Or it cost too much. Besides, I like making stuff!
Step 1: Materials
This is a semi-firm camera case from the dollar store. Try to make sure that it has two zippers so you can zip up to the headphone jack. If not, you could always get a case with one zipper and make a separate hole for the headphone.
Camera case $1
For the strap I used an old backpack strap and had some velcro sitting around but if you have to buy them, they aren't expensive. You can buy straps and velcro from the dollar stores but try to find them for free if possible.
Step 2: The Strap
The velcro was sewn on to the end of the straps. There are no dimensions because you'll have to determine the length for yourself. The strap should be able to go around your arm twice. If you don't know how to sew then hot glue might work or you could use other forms of fastening like tying, buttons, snaps, etc.
The strap doesn't stretch. I tried that but it constricted around my arm cutting off the blood flow so now it's a regular strap.
Step 3: Put It Together
The camera case has a belt loop and I just looped the strap through that. The reason for the strap being able to go around your arm twice is that if the velcro (or whatever fastener you're using) lets go, the pouch won't just fall off your arm. One loop will still hold it while you fix it.
There's not much to this but it does work quite well. I put it up just above my elbow and it's fine there. Originally I had it on my bicep but my muscles got bigger and the strap isn't long enough anymore!