N.C. Switching 5V using 12V. FET?

[vv_eev]

The target is a 5V line (4.3 to 5.5 VDC) which already gets grounded by a physical switch to trigger an action.  It sinks 4.5-5 mA @ 5V to ground when active.  Current is limited by the source.

I need a normally-closed switch in series, which will open with application of anywhere from 12 to 15 VDC (it varies uncontrollably). This will prevent the 5V switch from having any effect.  I can't draw more than ~25-50 mA from the 12V line.

Can someone help with the schematic and specs? And the math?  I'm so rusty since I ended up in firmware!

[inse]

PMOS transistor + 10k pull down resistor, two components
Switch over or NC reed relay, one component

[vv_eev]

Danke. Schematic bitte?

[Benta]

How about a simple relay?
Example (draws 9 mA @ 12 V):
https://omronfs.omron.com/en_US/ecb/products/pdf/en-g6k.pdf

Rugged, noise-resistant, cheap (~1.5 $ in single qty.)...