Multiple motion sensors for multiple led strips wiring
You can do this with four diodes:

But you need to find out what size diode part you need to dissipate any heat generated by forward resistance. This will depend on the current used by the LED strips.
This circuit isolates the sensor outputs from each other. If the sensors are tolerant of back-feeding when switched off, you can replace the two diodes marked &quot;*&quot; with wires.
If you can't or won't use diodes, you can use a 12V DPDT relay -- a very commonly available part.

Here you can see that when the &quot;stairs upper&quot; sensor is off, the &quot;lobby&quot; sensor controls the &quot;lobby&quot; LED and the &quot;stairs lower&quot; sensor controls the &quot;stairs&quot; LED through the normally-closed (relaxed) relay contacts.
When the &quot;stairs upper&quot; sensor is on, the relay steals the LED feeds from their respective sensor outputs and connects them both to the &quot;stairs upper&quot; sensor output through the normally-open (energized) relay contacts.