[1Jumper10]

They attach directly to the outside of the cylinder and sense the magnet in the piston through the cylinder wall. I recommend you get the cylinder and sensors together. They are kind of a matched set. Electrically they aren't anything special, just hall effect sensors, but their shape helps make a secure attachment to the cylinder. Also, a lot of cylinders already have the magnet in the piston. You might be able to get any suitable hall effect sensor to work.

[Al_The_Man]

They are only made for pneumatic generally. As these are usually aluminum cylinder, the hydraulic kind use a steel cylinder usually and the sensors I mentioned in PM do not work on these.
Magnet senors do not work on steel.
I have several 2 wire kind with LED indicator.
Often they attache with a jubilee style clamp that can be adjusted for position on the cylinder.The piston carries a magnetic ring on it.
Al.

[gudini_m]

Just an awesome thing, I feel sovereign) The signal on the radio catches perfectly, I work from any corner of the apartment. The principle of operation on the relay. -minus: The outlet from the network itself is enough somewhere ~ 5w, there is a slight heat. - the design is not thought out a bit as it is not possible to stick a filter in the network next to two, which is too thick; So only once,
I disassembled one socket on the button for the computer to turn it on remotely. As a result, from yusb through the booster filed somewhere 15v directly after the diode (this was enough for the relay to work, initially it was more, the volt ~ 24v could be mistaken already forgotten)) and it already consumes 0.3w and then with the relay closed, and of course it does not heat up .