I have been playing with the idea of a spring tensioner after looking for something online to purchase, and not finding anything I found worth the cost.
The biggest challanges so far with lock picking would be tensioning. I have read from someone more experienced mentioning "picking locks is 80% tension, 20% pick". While I don't have the accredited experience to validate that completely, I can say that after gaining more control over my tension, my success rate has increased.
To work on the idea, I used a paperclip to mock up what I was after.
I was actually pretty happy with just the paper clip until I decided to try and quinch it to make it more ridged, failing horribly after not being able to give it even heat with my butane soldering torch, making it go softer rather than harder.
After loosing what actually was a decent tool to failure, I decided to make something else using a different material, and this is what I ended up with below.
To fabricate it, I used steel from a wiper blade provided by my nieghbor. This particular wiper had two smaller pieces rather than a single piece, which worked out to my benefit for smaller locks and TOK (top of keyway) tensioning. While I did cold bend this, my other tensioners I used a tea candle to add heat which turned out to be a better way to go. To achieve the some what of a circle, I used a smaller sharpie pen and bent it around. It did go as smooth as I would've like as the bending a a crucial point didn't stay concentric with the pen, making it a bit off side.
I found having a 90 degree angle between the keyway and leveraging end was the best was to go, however have had instances where exceeding 90 degrees helped with lighter tension and control on more finicky locks. The nice thing is either way, you can lightly spread them apart or bring them together to change that with ease.
Over all, super happy with this tool and is the first one I grab. I plan on making more with different thicknesses of material for different keyway sizes, as I truely do enjoy it that much.