@alexsh1 Noted for the de-soldering info. I get it.
For voltage measurements, yes I did measure the voltage between the ground and the output pin of the motion sensor: when the pin is not connected to Arduino, I get 3V when motion is detected and 0V when no motion.
Then I connect the output pin of the PIR to the Arduino (pin 3) and I measure on Arduino pin 3: I get 3V when motion is detected and 1.2V when no motion.
As for the modification of the PIR: noted. But I mainly use the mini PIR, where such modification cannot be applied (as the circuitry is very different and very simple).
For the cabling: when I load on the Arduino the Serial Gateway sketch, everything works well, the Gateway starts properly, meaning the radio is well connected.
When I load the motion sensor sketch, it start properly, finding the right "parent" and immediately after this, there is a flow of info going out of the Arduino+sensor, sending 0s or 1s, constantly (like if there was an issue with the interrupt process).
And what I do not understand is that this (these) sensor(s) has(have) been working well for a while.