Why would you want this? To tweak animation speeds, enable USB debugging (for app testing or data recovery), or force GPU rendering on that rugged screen.
Here’s an interesting, step-by-step write-up on enabling on the K-TOUCH i9 (a rugged, industrial-style Android phone). Unlocking the Hidden Toolbox: Developer Options on the K-TOUCH i9 The K-TOUCH i9 looks like a walkie-talkie married a smartphone. It’s tough, loud, and built for work. But under that rubberized exterior lives pure Android. And like any good Android, it hides a secret backstage pass: Developer Options . How to open Developer Options in K-TOUCH i9
Now go forth, enable that USB debugging, and treat your rugged i9 like the developer-friendly beast it is. Why would you want this