Can I just raise a question about Slow cookers and leaving them on while you are out?

Any firemen about?

I saw a programme on Television the other night and the fireman said one of the common causes of fires in the home was leaving mobile phones charging
Would this not also apply to slow cookers?
I personally never leave anything on but the fridge The story illustrated on this programme was the fridge catching fire during the night
The old couple involved did escape but slow cookers have always worried me (as have washing machines and dish washers) If you are out that may seem OK but most of us are attached to other homes n London

If such a thing did happen then I am assuming home insurance would be invalid

I did once check with the Fire brigade about leaving appliances on during a thunder storm and they told me everything should be switched off and unplugged