There’s actually a decent amount of research into exactly this sort of thing, called, appropriately, “energy harvesting”. Depending on the application, it can be fairly effective. I know that vibration energy harvesting has been successfully in machinery monitoring applications, for example. I haven’t looked much into stray EM harvesting, but I’m sure it is possible…most likely to supplement a primary energy source rather than as the main source itself. But, yeah, for sure it’s an interesting topic with a fairly good amount of study into it…I think the University of Michigan had a few good research programs related to harvesting for ultra low power applications. You night check out some of what they’ve done

Try not to suck any cop dick on your way across the parking lot.