SDR made me understand how much RF noise my desktop computer emits. Lots of spikes between 400-500mhz. Could be my monitor also, as scrolling text seems to emit the most noise.
A really basic loop of wire is a directional antenna, so you can narrow down exactly what is causing issues too.
I'm doing it to find noise issues for my ham radio setup, but it can be generally fun. Not quite an SDR, but to find noise sources it's pretty amazing for so cheap.
It's bad enough that I lose several channels on my Samsung TV when my Samsung monitor is on if the TV antenna is in the same room as the monitor.