Open source and secure alternatives for some of these:
- Voice activated smart speaker: Mycroft (can be purchased as a complete unit, or DIYed with a Raspberry Pi and microphone+speaker array) https://mycroft.ai/
- Zigbee (the wireless protocol for smart lights and other smart devices) bridge: Conbee II (this takes the place of a Phillips Bridge, for instance. And is in many cases better because it works with all brands of smart light that use Zigbee--which is almost all of them, including the cheap IKEA ones--and also works for devices that aren’t lights. Cannot really be DIYed because Zigbee needs special hardware, not just software) https://phoscon.de/en/conbee2
I don’t know any alternatives for locks, vacuums, thermometers, or anything else sadly. None of these are that difficult to set up with just a little bit of tech know-how, and extensive guides already exist for almost all problems you could run into because the open-source community is almost psychotically dedicated to its projects, unlike Amazon, Google, and Apple where it’s practically impossible to get help with any problem that’s even slightly unusual.