does the frequency emitted by the keychain remote change by any measurable amount? If so how fast would I need to be moving towards or away from my car before the remote no longer functions?
Thanks!
Usually a receiver is can pick up a range of frequencies, falling off in sensitivity from the exact frequency it is tuned to. IIRC this is called the q value of the receiver. The higher the q, the narrower this range. (keeps you from picking up other signals on other frequencies). Usually a receiver will be still be able to pick up a signal that is within .1% or so of the center frequency. ( Why FM radio stations are about .2% or .2 MHZ away from each other)
So as long as you aren’t moving so fast that you redshift the light by more than .1%, you should be fine. At this point I need someone else to step in and calculate how fast this is. However, I am quite sure that you cannot run that fast. I imagine you have to get into the speed range where you start measuring things in kilometers per second before you’d have a shot.
To change the frequency by a factor of 1.001 (increasing by.1%) you need to change the wavelength by a factor of 1/1.001 ~ 0.999. That is, while the first peak of the radio wave has moved 1 wavelength, you need to have moved 0.001 wavelengths. In other words, you need to be going at least 0.001 times as fast as light. Speed of light in air ~ 3E8m/s. So you need to be going 300,000,000m/s*0.001 =300,000m/s =300km/s
We’re talking astronomical speeds here. IIRC when people measure frequency shifts in light they need to use interference pattens or crystals with very specific frequency responses, which can measure much smaller changes.
Thanks Shade, I knew it was something simple, but it was escaping me at the time.
Thanks, but hold on: I’m not certain I’m right. I’d feel a lot happier if someone checked my naths. Then again, I’m fairly sure that running fast enough to not be able to get into his car would make that the least of his problems compared to, say, exploding due to atmospheric friction 
I’d say you are pretty much on; we don’t know how much of a shift would throw the car, but the example given is close enough.
I wonder if dopler-boy also worries that his shirts change color when he runs or that he increases in mass… 
Your naths look fine to me Shade 
V
Thanks.
A sign supposedly on the door of a physics department, written in red: “If this is in in blue, you’re going too fast.”
Perhaps he’d have better luck experimenting with sound waves. There he could make a difference.
Oh, and Vetch, normally I like to get to know people before they compliment a Nath, but I’ll let this one ride
I have nothing useful to add, especially since the question’s been answered; I just wanted to point out that I’ve been on the SDMB too long – my first thought upon seeing the thread title was “he’s trying to redshift the remote’s signal.”