What does the Alarm Remote Chin Trick do?
 

I'm not sure if it is common knowledge, but among my friends at least, and in my personal experience, you can nearly double the range of your car's alarm remote by doing the 'chin trick': pointing the remote up under your chin towards the back of your head and hitting the button.

Anyone else have any experience with this?

I assume this uses your skull as some kind of parabolic reflector, but I always wondered if anyone had done any research about this, or had any links to pages with info on it.

are you sure? never heard of that. maybe someone can explain why this work in specific ~

Hm...all I've found on google is people reporting that it worked for them, and some vague guesses as to why.

Works here, always has.. ...gotta be like an organic inductor..

Who knows...

-SF

antennaes and wavelength.

Your body becomes an antennae which provides more gain and directional signal.

This is an odd effect.

Antenna theory essentially states that the antenna must match the wavelength (be it whole number or fractions) .. and with a frequency of say 45MHz [average for most "non-IR remotes"], the wavelength is 6.67m (lamda = c / nu; where c = 3.0e8m/s and nu = 4.5e7s). The most efficient antenna tend to be: full wave, half wave and quarter wave antennae which means: 6.67m, 3.34m, 1.67m

Average human height happens to be 1.6m [5'6"] (which is the quarter-wave for 45MHz). Wow! So, using a human body, the ideal quarter-wave frequency is 45MHz.

*note to self* :hmm: *evil grin*

So the average human body _could_ act as a passive reflector ..

I always figured it was some sort of antenna effect... I never really believed it worked until I got a new car and the remote has a painstakingly short range... how do they expect me to find my car at night in a crowded parking lot when I have forgotten where I put it? the chin thing usually does the trick.

Thanks sapper.. i was thinking along the same line (the atenna) but thanks for explaining in detail. Now the question is if it 's bad for you.. lol pointing that right into your chin might kill some brain cells?

Yeah I heard that it works and I havce tried it with varying results positive and negative. I just assumed antenna. Who knew?

Funny you should ask :D

All phrases which are bold are key scientific terms - worth further research to any interested.

All chemical compounds have what is called a bond dissociation energy which basically means, given 'x' amount of energy, the chemical bond will be broken.

In DNA, a relatively weak (but very important) bond known as a hydrogen bond is used to hold the double helix together. Phosphodiester bonds (stronger than hydrogen bonds) hold the A,T,G,C nucleotides together along the length of DNA. If any of these bonds are broken, DNA replication errors _may_ occur - which if left un-checked = mutations. In the worst case, phosphodiester bonds are broken and a very damaging mutation known as a frameshift mutation occurs. Thankfully, DNA is very good at 'proof-reading' these DNA transcripts. To give you an idea .. for every 10e9 (read 10 to the power of 9) correct base pair (A-T and G-C) combinations, only 1 or fewer (zero) will typically be wrong. Furthermore, because of the huge portions of non-coding DNA (introns), it is very unlikely that an exon (protein coding portion of DNA) will be affected.

Going back to the question, a typical hydrogen bond has a dissociation energy of approximately 436 kJ/mol (4.36e5 J/mol) which means roughly 7.24e-19J per bond.

According to Plank's equation, the energy of one photon can be calculated as: E = hv (read: energy = h times 'nu') where h = Plank's constant (6.63e-34Js) and 'nu' = frequency (s^-1)

E = (6.63e-34Js)(45MHz)
E = (6.63e-34Js)(4.5e7s^-1) {seconds cancel leaving only Joules}
E = 3.0e-26J per photon

As seen above, the energy required to break one H-H bond is 7.24e-19J whereas the radio wave can only supply 3.0e-26J per photon .. this is a difference of 7 orders of magnitude (lots!).

Long answer, I know .. but here it is:

The radio wave should not be able to break a typical H-H bond in DNA.

As you can see, there is a vast array of scientific mumbo-jumbo behind this answer .. and it could get even more complicated if you really dig deep. For any who made it this far before turning off their computer, skipping to the next thread, or so on .. I highly recommend you have a quick peek at all the terms I "bolded". :D

Cheers! :p

This alarm chin trick thing is the same thing as why when you grab your TV antenna the reception sometimes improves.

As for whether this harms you I say no way because the transmitting power and frequency of the alarm transmitter is small (100 ft. range approx.), especially compared to cell phones. When you get up to frequencies like 800+ MHz, which cell phones use, the signal can penetrate and the molecules in your brain can actually kind of vibrate causing them to heat up and potentially cause damage.

This last reply is somewhat misguided.

The amount of energy that a wave can expend is a function of its frequency. Power is a function of energy.

Without getting too involved in the details, any higher frequency wave will typically have a greater energy, thus power .. however, power is also a function of transmission area and angle of adsorption (d not b).

If you really want something to worry about - it should be UV light - it has enough energy to cause rampant mutations in DNA - specifically frameshift mutations.

To nit-pick on the "vibrating brain molecule" theory - microwaves work on the principle of rotating water molecules, not vibrating them. The only reason a microwave works is because the resulting wave resonates at the same frequency of water. The real danger with wave forms is definately bond dissociation.

:D :p

[Edit: Had to add - > Science Rocks]

Would this also help to explain why tv or radio reception seems to improve when someone is holding onto the antennae?

Sapper,

Out of curiousity, can I ask you what is your field of expertise? You are obvious well versed...

Let me elaborate a little bit on where I am coming from with my response above :), I am coming from an Electical Engineering background. Hopefully I don't ramble too much as well...

The amount of power produced by an EM wave is absolutely a function of it's frequency...but also it is a function of the Magnetic and Electric fields of the signal, which at least in the case of the E-field, is really only the gradient of the voltage. In fact, the 'Poynting Vector' S = H X E (vector cross product) is the power per unit area carried by the wave and is a vector in the direction of propagation. From that we find that the average power in a lossy medium, we can be liberal and say that our brain has SOME degree of conductivity, is:

Sav = ((mag. of E field)^2)/(2*intrinsic impedance of the medium)*e^-2az*cos (angle of absorption)

a is alpha which is the attenuation constant of the wave, which is the frequency dependant component. z is a displacement from the wave front.

Therefore, if you have say a 125 mW signal, that is having to due with the voltage at the propagation source (antenna), then that is a factor in how much energy your head will absorb.

Now, the FCC limits peak RF power exposure to 1.6 W/kg of tissue. Therefore, in the case of cell phones, which nowadays radiate about 125 mW and lower, since the antenna is SO close to the head, the exposure limits are sometimes approached.

Now since I am going to quote an article from IEEE in August 2000, which states that the energy in the frequency range at which cell phones operate is non-ionizing because the photon energy is insufficient to knock electrons from atoms in living tissue (as you have discussed in the molecular bonding sense), that is the source of biological damage from X-Rays and stuff. But, the most apparent biological effects of RF energy at cell frequencies is due to heating. I assumed that the heating was due to vibration somehow, but now I think it is something simpler....I am trying to figure that out know, maybe you have any ideas????

You too are obviously well versed in wave physics - my background is Biotechnology w/ specialization in biophysics.

I was really hoping to avoid the E + M wave aspect actually. :D
Looking at the vector cross-product function above, I assume that H is the magnetic portion of the wavefront?

None the less, the "power" can still be calculated through basic wave-equations (similar to simple harmonic motion). As you correctly noted, the RMS values are used as opposed to absolute.

As you stated, the frequencies involved are non-ionizing and thus are unable to cause bond dissociation (hence the non-polarizing).

The trouble with the heating argument is that the human body is highly adapted to thermoregulation. As you are surely aware, the average specific heat capacity for the human body (similar to water) is 3470 J/kg'C. In short, we are great heat-sinks. Furthermore, the thermal conductivity of human tissue (excluding blood) is 0.2 J/s'Cm (Joules per second degree metre) and blood has a thermal conductivity of approx 0.4 J/s'Cm.

What does all this mean?

As a body part is heated, the heat is moved fairly efficiently through out the entire system - then into the surroundings. All the data I have seen regarding near-range radio transmissions have produced such little energy that even assuming 100% thermal adsorption, the heat would be conducted and transported away at a rate exceeding the rate of input.

As I am sure you are aware, the thermal adsorption would be well below 100% and so very little energy is transfered.

Again the question though: how would the tissue be heated?

As a point of interest, I will look into the resonant frequency of cytosol (in a simplistic sense, the "goo" that is the cytoplasm of a cell).

I asked a close friend of mine (physicist) about resonance of particles based on quarter, half, etc-wave frequencies. The principle of maximum heat-transfer is dependant on distance between antenna and medium. As an example, microwave ovens have a wavelength of 10cm and thus, maximum heating ocurrs at 10cm, and other "efficient spots" would be 5cm and 2.5cm. It seems that the frequency plays a major role on the areas of tissue which would receive "maximum heating". Interesting.

All said, we would have to start looking into the thermodynamics of the system (tissue) and the surroundings (body) to better understand the issue.

Coming back to the 45Mhz transmitter question: these devices are such poor transmitters (low power) that I would expect you could heat a glass of water from 20'C to 21'C in about 10 years (assuming no loss of heat to the surroundings). I wouldn't worry. :D

I've never heard of that. Quite an interesting concept, but I've always been kinda leery of pointing lasers and the like at my head! I've got enough problems as is, I don't need "laser brains" on top of it!