The physics of car alarm remotes

I thought of this as well. I’ve never held my RKE to my chin (this is a new one on me) but I have frequently held it above my head or generally waved my arms around mashing on the button hoping for a good signal to my car. I’ve never tested this in any decent manner to see if I get better results this way however so I may just be acting a fool for no good reason.

As to your post I don’t believe you need a direct connection from your body to the antenna. The little unit broadcasts and in some fashion your body picks up the signal and retransmits. This of course is a WAG on my part…just tossing stuff out there (and, frankly, it sounds weak even to me…I’m just bored right now).

That your body can act as an antenna is probably common experience to all of us who are about 25 years old or older. Ever grab the rabbit ears on your parent’s tv to get better reception?

I don’t buy that and have proven (to myself–unscientific, but repeated trials) several times over the years that it isn’t height. I have tried holding mine over my head as well as under my chin. It simply works better under the chin for some reason. I don’t know if the cranial cavity is acting as some sort of passive repeater, or what. I DO know that it works and I have used this method for about 10 years, wondering why the whole time.

I want to know what chriszarate named this thread.

The physics of my doohicky?
The physics of body cavities?
The physics of flesh?
The physics of finding a car?

And, I want an email notification when someone posts the answer.

What about this. Do those of you who claim a dreastic improvement have much dental work? Ever been abducted by aliens?

Perhaps your head is acting as a resonant cavity or a waveguide of some sort? What frequency do these remote controls use? A part of the spectrum of microwaves have wavelengths about the diameter of a human head…

Never thought much about this. I always just looked at the Row sign to see what the number was at the location I parked my car. I’ve seen other people do this…had about a dozen car’s, all chirping at the same time.

This kind of remindes me of the two aggies that went to a Rice vs. A&M game on a camel…so they would not need to look for their car.

For the record, I ran a little experiment last night with both of my vehicles. I found no improvement in range from using my RKE from under my chin (with mouth open - boy did I feel silly, but it was in the interest of science) versus held at arms length at chin height. I did find slight improvements from waist high versus head high versus with my arm extended over my head. In other words, the higher the transmitter, the better the range (but only slightly) - no big surprise.

Chronos, thanks for correcting me. Microwaves are indeed non ionizing. I appologize for the misinformation.

Well… I am not nearly as well versed as some respondents to this thread in terms of the physics of RF broadcasting, however, in my mispent youth I was a Radio Shack manager and can attest to the empirical observation that RF emitting devices will do any number of odd things. Having said this, however, I cannot see how the under the chin placement is going to do anything to increase range vs holding it at the same height elsewhere on the body.

From the perspective of an RF wave (nothing personal) you are simply a big bag of salty water. While the body can help to amplify or pick up (and possible transmit) RF signals the under the chin placement should have no measurable difference vs, say, putting it on your bare shoulder at the same height. I think the fact that it is pressed against your flesh is a lot more important than the fact that it is proximate to your head if the body=better broadcast antenna hypothesis is valid unless your mouth is full of silver amalgam fillings, then all bets are off.

This sounds like an excellent topic for a kid’s science experiment that you could do in the parking lot early Sunday morning before the cars accumulate. I would suspect that height and not body orientation is the primary determinant of range

There are three ways you might get an improvement with the chin method:

  1. Increased height vs. pressing the button at waist-level. This will definately improve range if it gives the transmitter line-of-sight to your car.

  2. Better directivity- the antenna inside a keychain remote doesn’t radiate equally well in all directions- there’s some directivity to it. By holding it in a different orientation against your chin vs. your hand at waist level, you may be aiming the antenna better. This would be a hit-or-miss effect, but would be consistent for an individual, if they always held it the same way, and faced the car each time.

  3. Using your body as a ground plane. Many antennas will work better if they’re radiating against a ground plane. For the purposes of high-frequency RF, your body conducts enough , and may be enough of a local ground to act as a ground plane. In effect, this boosts the signal in the direction away from you, at the expense of signal strength in the other direction. You should be able to achieve the same effect with your shoulder or other body part of similar shape and mass at the same height. A sheet of aluminum foil might work even better.
    Arjuna34

JoeyBlades, Arjuna34, astro, et al, thanks for your replies. I am e-mailing my uncle the URL to this thread, I think he’ll be blown away. Then again, he’s a lawyer, so he might just sue all of you. :slight_smile:

Chronos, I think I originally titled it “The Physics of Car Alarm Remotes”, but I think I might like doohicky better. Not really, though.

inspector3500, I am a Rice alum and must tell you that some Texas fans a few years ago came to a game at Rice on a horse, and after the game seemed to be helping people find their cars.

Thanks all!

Do you have metal fillings?
Have you heard of those people who get radio stations in their head because the fillings pick the radio waves up?

You know, you guys mocking the true believers are really, really funny.

I had a friend who had a cheap ass Radio Shack remote. Remote at waist level, head level, above the head, aimed at the car, aimed at the body, etc, and the range was just over 10 yards. Put it against your body (anywhere, although we always used chin) and the range was better than 30 yards.

I use a Sidewinder 6500HF (high frequency) unit, so range is NOT a problem. Mine goes over 100 yards, tested. (Roof on top of 36 floor building, a block away, and my car started)

–Tim

[sup]Tangents away…[/sup]
inspector3500, were these the same Aggies who got to Hempstead and saw the sign saying “Houston left”, so they turned around and went home…?