Hello,
thank you very much for your answers!
@jroorda: This is an important question to ask. I think other factors should be regarded more than the encrypted wireless transmission that might be an overkill, as I understood the answers like. It has to be reliable always.
Maybe the thief is able to jam the transmission frequency, because he thinks that will avoid the base station getting the "alarm"-signal, but in fact he just prevents my "OK"-signal to reach the base station and that will result Alarm before even getting in. This is also a problem because this is a false-positive, the alarm can be triggered without making physical damage. Do you think this is a problem for the system?
@djjoshuad: I read your long answer with interest and I think I will concentrate of those 99% of burglars that are not electronically skilled. However, I think it is not able to get the key behind the rolling technique, Rolling code - Wikipedia, the free encyclopedia, RKE Analysis, a replay attack will fail because the "OK"-signal always changes.
@wildbill,PeterH: I am still not sure whether I should add encryption to the system or not, it also makes the system more fragile because it is not simply get-ok-signal or not get it, but also checking whether the decrypted counter is in a specific allowed range.
For me the wired solution would be a sophisticated one because the alarm station and the base station are in different floors and cable laying doesnt look that nice and is difficult to hide.
I am not only interested in the factor of wireless signal but also others like the alarm device (siren, strobe,...) For that I am planning to do the following:
If the cable is cut, the lightblue cable is also cut and that is recognized by the Arduino, but how to trigger the alarm then if you know you cannot trigger it?!