When I built my router, I added an earth continuity wire through each cable chain, connected to the metalwork at each end, to ensure a reliable connection mainly for this reason. I use a normal water-cooled spindle and have never had an issue. I use a small piece of tooling plate on a length of wire as a sensor. I also installed a fixed touchplate just below bed level although it does occasionally get covered by larger pieces of work so can't always be used.

One reason for using both is that sometimes you lose the reference surface after a machining operation which makes it difficult to set the height for subsequent tools. I wrote a few macros to do things like pick up the work reference with a tool, then move to the fixed plate to record that height wrt the work, so I could use the fixed plate for second-op tooling. In practice, it all depends on the kind of work you do - if you use spoil board height as the reference, for example, there's no need for this approach as the reference surface doesn't go away! With a simple "complete the circuit" type of sensor, wiring the two together is trivial.

On my CNC mill, I use a simple 3D probe for height setting of the work or other reference, but also have a bed-mounted tool height sensor. I have added and modified macros to, again, probe work height then find the tool length via the tool height sensor. During subsequent M6 manual tool changes, tool height is automatically set off the bed sensor. Have to say that the two-sensor setup is used a lot more on the mill than the router.

Can't say what make the tool height sensor is, though, as it came with the machine and is unmarked.