I have thought about this from time to time. I want good surveillance, but I also don't want to lose control of the video.

I think that the solution that I favor right now is a Wyze cam V2 or similar flashed with openmiko. edit:(I had to buy wyze v2 cameras from the US on ebay to get v2 versions, user:@ashok36@[email protected] suggests in this comment to use v3 and Wyzemini firmware - this might do the job. clarification: the point is to replace the manufacturer's firmware which will phone home with something open source that you could audit)

These can be attached via USB or wifi interface to a server with zoneminder (https://zoneminder.com/) From there you could think about offsite records too and motion detection etc. [edit: wifi is useful as I don't want to rewire the house - though could be blocked (or the router could be unplugged!) if you are expecting technically savvy criminals. A solution here would be to use an old router on a separate wifi network, put somewhere where most of the property would have been traversed before it could be accessed (e.g. upstairs).]

Having said this, the setup is just fiddly enough that I keep to finding myself finding other stuff to do. [edit: 'Fiddly' is the wrong word, I think its pretty simple, I just find myself wanting more features until the project doesn't happen at all. I'd be clear that this is a feasible DIY project, so long as you accept that 'done' is better than 'perfect']

[edit: One last note - if you host the video yourself, you take responsibility for the security - this means keeping zoneminder and the OS up to date and offsite backups/networks/cameras secure. This is possibly something that a company is better at (but don't bet on it!). However, you are also a smaller attack target (because bad actors only get your video) so blackmailing you with whatever you do in your surveilled place is less valuable than having the same data for 1000s of people. Also, if someone has access to your home network - they can set up man-in-the-middle attacks and steal your bank details - you have to be doing something interesting in front of those cameras for it to be worth more than the contents of your bank account.]

edit:clarity/details