Aluminum wiring is perfectly safe so long as it's not connected to anything. Unfortunately, my house has aluminum wiring and it is connected to things.
I found out during the home inspection. If you Google "aluminum wiring" you will find all sorts of horror stories, which is exactly what a stressed-out house-hunter loses sleep over. Which is what I did. There's some controversy about aluminum, but it seems to be well settled that it's a fire hazard. The controversy is over what to do about it. I won't vouch for the source, but Inspectapedia sums up the issues.
I couldn't afford to totally rewire the house. I also couldn't afford to die in a fire.
Eventually I was comfortable that aluminum is "safe enough" if all the outlets and switches have some mitigation in place. You have to use outlets and switches that are made for use with aluminum. They're a little more expensive. Some devices aren't available in aluminum-compatible varieties. I wanted several GFCI outlets (the ones that don't kill you if you drop your toaster in the bathtub) installed, but there are no aluminum-compatible GFCI outlets. The electrician would have to "pigtail" copper wires to the end of the aluminum, then connect the copper to the outlet. Pigtailing is its own mess.
The only unambiguously safe pigtailing technique is the steampunk-inspired COPALUM, which is expensive and not always available. AlumiConn connectors are promising, but don't have a long track record. The most commonly used is Ideal Twister #65 purple wire nuts, but some of the scarier anecdotes suggest problems.
The electrician didn't know of any problems with the Ideal wire nuts. In a flurry of smugness, I decided that made me better informed than him. So I told him to use AlumiConn connectors even though he wasn't familiar with them. I'm the kind of customer I hate when I'm dealing with customers. Me with my two nights of Googling, and him with his something more than that.
Eventually, I realized that my opinion is rubbish, and that having people use equipment they aren't familiar with isn't how you make things safe. So I told the electrician to use his own judgment, which was the Ideal wire nut. I haven't died in a fire.
It cost about $900 for two guys to A) verify that every switch is aluminum-compatible, B) replace every outlet with aluminum-compatible, and C) install several GFCI outlets.