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12v device to switch on a 9v device (signal to switch on only)

I have a device that is switched on by a sensor, powered by 12v, 1.3amp battery.
I have another device that is switched on by a mechanical push button switch, this is powered by a 9v battery.

I want to piggy back on the wires that switch on the 12v device and take the signal (to turn on only) to the device that is already powered by a 9v battery and normally turned on by a push button switch. ( I want to replace this mechanical push button switch with an "electronic switch" turned on and off the the presence and absence of the 12v signal)

I want the 9v device to switch on only when the 12v device switches on and switch off when the 12v device switches off. Also I want the 9v device to only run on the original 9v battery (not accepting power from the 12v device and not returning any power from the 9v device to the 12v device.

Is there a switch device/relay that can do this? A device that I can just connect between the wires going from the 12v device to the 9v device?

I am a novice to electronics please be kind. I an open to using part from another device, and basic mods.

Thank you

Just use a little 12V relay. 12V refers to the coil voltage. Use the relay contacts to interrupt the battery of the 9V device.