Our house is festooned with old surveillance cameras that the previous owners thought desirable, but which we thought looked, frankly, utterly paranoid and bonkers -largely because there were half a dozen of them! So we've never used the pre-existing surveillance infrastructure. After a spate of local break-ins, however, we thought it might be a good idea to have some video surveillance after all -just not in quite the loony way our predecessors considered suitable!
In the shower one day (too much information, I realise!), I had the idea that the drawer-full of old smartphones we possess but never use might be put to good use with a bit of ffmpeg or similar Linux cleverness. What started as an idle thought in the shower soon became a bit of a project, however, as smartphones are not ideal webcams and ffmpeg isn't easy to get to grips with!
In the end, I put a simple two-camera system together (with a freshly-bought, second-hand 2012 i3 PC) for around £120 and the results are pleasing …though still require a bit of tweaking in the days and weeks to come, I suspect.
There was then a bit of a scare when a neighbour suggested I might be in breach of the GDPR (new European privacy regulations), but a bit of research there made it clear that the GDPR is not an obstacle to running a domestic CCTV system, provided you follow a couple of simple rules/guidelines.
Anyway: I wrote the entire thing up as a bit of an article, which can be found here.