single positive pulse to constant on/off?

I'm looking for the cleanest way to take a single positive pulse from the OEM alarm/central locking system to toggle power additional sensors and warning LEDs etc. The pulse is provided when doors are locked, and unlocked. I want to toggle the power to other devices from this. I believe this can be done with a single relay? But I can't find a latching relay that does this apart from one made by VW which they used in early cars to switch between dipped and main headlight beams. I would like to use the least amount of relays etc and I would also like to keep drains down. I believe the wiring diagrams shown on this site so far requires the relays to be constantly energised for them to work? An advice welcome! Thank you.

From momentary to latched output...

But that's 2 buttons! Otherwise I would have provided the normal SPST latching relay wiring.    (It can follow the input power, else an optional switche to engage, or an optional switch to break. The same topology as your SCR diagram except with an SPST relay...) POST EDIT - the same as your 2nd diagram with a single relay; though I include diodes towards 86 to prevent cross-powering (instead of the otherwise redundant relay in the last 2-relay version). That circuit is often used to limit switches - eg, water level systems.

Oh wow lol... I was thinking more along the lines of a mechanical latching relay!

The problem is the single input/switch. Two switches is easy.