If it’s really an aluminum gate, you’re probably going to be OK depending on the exact angle back to the house.
Metal gates can potentially cause two completely separate problems for an open/close sensor.
1) Confusing the sensor.. If The metal is magnetic, which means iron or steel, then overtime the metal parts near the magnet when the gate is closed can themselves become magnetized, enough so that the reed part of the sensor gets tripped even when the gate is open. This can be a real challenge.
However, the good news is that aluminum does not magnetize in this fashion, so it’s not likely to be a problem.
2) Blocking signal. That said, metal, including aluminum, can block RF signals, making it difficult for the radio in the sensor to communicate back to the house. This is due to a different physical property of the metal, the fact that it is an electrical conductor. Anyway, physics.
The signals are Omnidirectional (360°), but they spread as they move away from the point of origin. So it is possible that you might place a sensor in such a way on a metal gate that very few signals would get through to the other side of the gate.
This is something you can just play around with. But probably if you can put the radio part of the sensor on the interior of the gate so that signal doesn’t have to pass through the gate to get back to the house, things should work OK.
As far as the in-frame devices like the sensative strip, it will probably depend on how much of an air gap there is at the point where it’s placed as far as whether you’ll still be able to get signal back at the house. But I think it’s definitely worth trying. 