If you want to stop someone copying your electromechanical product -and selling it as their own, you could try obtaining a patent in that someone’s country. If you don’t have the cash, consider today’s invention.
Sensors within the machine’s casing would detect any attempt to open internal enclosures that weren’t required for normal maintenance/access. These could be wired to a hidden mobile phone which would alert you as manufacturer.
Rather than generating a ‘cease and desist’ letter, however, these sensors would automatically release a fast-curing epoxy cement within the enclosures.
One component of the resin would be impregnated with metal fibres, so that the device would short itself out before being encased like a fly in amber.
This tactic is reasonably cheap, poses no danger to anyone, but results in a collection of nonfunctioning bricks which is no longer cost effective to reverse-engineer.
Personally, in advance of any of this, I like the idea of having the phone say “This device will self destruct in five seconds…”