Use LED output to trigger an arduino?

I have an wifi controlled rc vehicle. I would like to use it as is, but need to activate 4 devices (in order). The easiest way I can see is to use one of the led "headlights" (can control turning them on/off via wifi app). I would like to rig it so the led turns on, it activates a device on d1 of the arduino, turn it off/on again it will activate device on d2, etc. Using an external arduino of course.
My question is, what type of circuit would I use to read the led's on off signal, read by the seperate arduino's digital input? I was thinking a signal relay. But don't have one handy for that low of a voltage. (2.73v and a few ma for the led).
Would it be easier to use a transistor? (have tons of 2n2222).
Any examples of a circuit I could use to accomplish this?
Thanks for any assistance.
Ed

The 2.73V is just a bit low to read reliably as high on a digital pin I think (needs to be ~3 iirc), but why not read it on an analog pin?

2.73/5 x 1023 is an analog value of 558 so maybe just look for it to be over 500 say? (Check that when it's off, it's 0....)

manor_royal:
The 2.73V is just a bit low to read reliably as high on a digital pin I think (needs to be ~3 iirc), but why not read it on an analog pin?

I spoke too soon. Measuring the voltage between the anode and cathode when the led is on is 2.73v, when off it measures 0v as expected. But using a common ground on the arduino and rc rover (power supply ground) the led when switched off the anode jumps to 7.2v! (the voltage of the power supply.)
I assume the cathode (-) of the led is transistor switched on the rc vehicle. So I am nit sure how to wire it to use an analog pin on the arduino.
Voltage divide on the led circuit?
Original reply-----
That is a brilliant idea. I would have never considered that solution.
I ran a few tests, mostly because I was worried about the voltage fluctuating and maybe triggering the switch/devices as the battery dies. It only varied by 0.05 volts at any load and just drops out to 0v as the battery dies. So that is the perfect option.
Thanks a million!
Ed

I ended up connecting a opto-isolator to the led from the rc vehicle. This methid works perfectly with the existing rc circuit.