Buy off the shelf sensors wherever they exist and fit, and we will tell you when they do. Building is for when nothing available measures what you need, survives the environment, or physically fits where it has to go.
The difference between a device that works and one that keeps failing is testing in the place it will live. Dust, damp, vibration, temperature swings and being knocked are what kill hardware, and none of that shows up on a workshop bench.
Power is a design constraint agreed at the start, not a surprise afterwards. Mains where the site has it, battery where it does not, with the expected life stated up front. Everything is updateable remotely, because a device you cannot patch becomes a security problem the day it is installed.
Bring us a plan or just an idea. We will arrange a discovery meeting with you to go through it.