This question already has an answer here:
I witnessed one of my settlements being attacked by super mutants some time ago and when I went to equip my Power Armour some sneaky settler had stolen it and was out fist fighting with them!
Is there any way you can make the power armour available to you and your companion only?
More specifically can I stop random settlers stealing my power armour?
I have temporarily caged my power armour within fences without a gate so that they can't reach it but that means I waste steal by trashing the fence when I want the armour!