We lived with quite safe electronics for quite a while so many don't even think about safety. If you experienced 230V AC through your body, you will think quite differently.
This is literally what currently prevents me from doing DIY IoT projects at home. I'm not proficient enough in hardware to build battery-powered items, and I'm scared of leaving unattended anything I built that's powered off a wall wart.
To loss the fear just experiment with some safety and take measurments. You can let plugged a new project during some hours to look if it makes nasty things or not.
Anyway, I really encourage you to doing DIY projects at home. Most of them work in low voltages between 5 and 3.3V, risks are close to nothing.