Emergency brake (e-brake, parking brake) systems in most cars are a purely mechanical system using a cable. In the passenger compartment the hand brake lever pulls two wires which have a direct cable link to a caliper on each of the rear wheels. The brake clicks because it ratchets and you press the button to release. Some cars have a foot-operated brake that are the same concept.
Basically all vehicles codes all over the world require a mechanical secondary brake to the main brake on the car and in general, manufacturers use the cable-driven approach because it’s simple and has proven itself over time. That said, many high-end car manufacturers now have electrical systems for this, but that basically just means there’s a serve which pulls the caliper. You can also buy emergency brake kits which are hydraulic, but these are not allowed in many jurisdictions for constructed vehicles. (The may be allowed for OEM, but I’m not sure)
Anyway, cable-driven e-brake it is. Reliable, proven, easy to adjust and maintain. But not that easy to install in my case. Here’s what I had to do to mount the caliper – cables have not arrived yet, so I’m holding off on the handle install until then.