It’s a neat hack, but you’ll need to be honest with yourself about power. A 2‑year‑old phone probably only has a 2000‑3000 mAh pack left, and a full‑bright LCD will drain it in a few hours if you’re running home‑automation daemons and a background OS. If you can keep the screen at a low brightness, disable vibration, and turn off everything not in use, you’ll get maybe 8‑10 hours of uptime. That’s fine for a weekend test but not for a “always‑on” panel. A better bet is to repurpose a tablet or a cheap single‑board computer with a small LCD, or even use the phone as a remote that’s plugged in. If you really want the phone, consider soldering a secondary battery or using a trickle charger so you’re not chasing the battery life. Either way, it’s doable, just don’t forget the power budget.

Sounds like you’ve mapped out the whole “phone‑as‑hub” death‑by‑battery curve already. I’d be tempted to sketch a quick table of power draw per feature—screen, Wi‑Fi, background services—to see where the sweet spot lies. If the numbers still scream “don’t do it,” that’s the signal to keep it in the drawer and go the SBC route. Either way, it’s a fun experiment; just make sure the wall‑mounted case can handle the extra weight of a backup battery if you go that path.