EMF and key FOB drain - possible?

My first inclination is: During FOB storage, either in your pocket, briefcase or wherever, one of the buttons is occasionally being held down.

I have a situation where I'm always hearing my car lock/unlock and arm/unarm because my car key FOB in my pocket is pressing something. I need to change it's default habits.

As a test, you could make no changes to how you store your home FOB, but rather, change your FOB battery then swap it with your wifes. Do that for a week or so, it may have something to do with you as opposed to the Prius itself.

The Prius cable voltage EMF is extremely low (which halves in power for each doubling of an equal distance) and I don't know that the Prius has any transmitters other than the Garage door opener (Homelink).

Try the FOB swap, see what happens.

ZC1

 

ZC1, the Prius has SKS transponders if the car is so equipped.

I'm a little confused, Steve, about which fob is failing, the Ingrid alarm fob or the Prius key fob? If it's the Ingrid fob, try replacing the battery, so you know it's fresh, and storing it in an Altoids tin when it's in your Prius. The tin box should provide sufficient shielding from any stray EMF or RF in the car.

I'm not familiar with the Ingrid system. Is it passive, like the Prius SKS system, so the security arms and disarms based on proximity, or do you have to press a button to actively change state? If it's active, there seems to be little chance that an external signal is somehow triggering it to be active and drain its battery, but putting it in a metal box to shield it won't hurt.

 

At least swaping the key fob with the wife may rule out or reveal a defective key fob and putting the home fob in an altoids tin while in the car may prove an EMF problem.
Never combine the tests, it makes the problem more vague.

I don't have the frequency information on the Prius SKS system.

 

If the house fob requires a button push before activation it is not actively listening for a signal, in which case the Prius fob will not cause it to drain. The Prius fob is passive and does not radiate until it hears a signal, although it can confuse other RF as a signal from the car.

Are you hearing beeps from the house fob at random times?

Try trading your fob with your wife's fob, since hers is known to be good.

Tom

 

Wasn't there a known issue with the Prius SKS fob and Shell SpeedPass?

 

I have a couple comments Steve.
I heard recently that keeping a cell phone in an RF-thight environment (like a metal filing cabinet or desk) will cause it to drain faster than normal because ti is always searching for its RF source. I don't know whether your Ingrid fob does this or not, but it might be worth consideration.

I can also imagine that a good test is separating the Ingrid from the Prius fob just to see if the battery in the Ingrid last longer (this may have already been discussed and I just missed it). It sounds like another good test is what you just proposed - trading with your wife to see if that makes a difference.

On the subject of acronyms (unrelated to the Ingrid drain problem): Years ago back in engineering school the term EMF stood for Electro-Motive Force (or voltage). Fields were more commonly referred to by other terms (flux etc.) and their impact on on their enviroment as EMI/EMC (Electro-magnetic Interference/Electro-Magnetic Compatability). However it appears that the recent advent of the metaphysicists (or whomever) have cause fields to be more well known and redefined EMF as the term you are using. It sure caught me by surprise. I guess I am getting too old.

 

EuroSteve,

Is there any resolution about this issue?

I suggested the wife FOB swap, while Bill suggested the Altoids tin test.

ZC1

 

If you're worried about interference between the two, try to see if they're on the same frequency (product documentation, etc.) You can tell when the fob transmits, since the red LED on the fob will light up. AFAIK, the prius dosen't have a 'retry' mechanism. It just dosen't let you in!

Prius Tx (from car to fob) is at 134.12KHz, OOK
Dummy me actually stuck an antenna in the car and looked for it on a spectrum analyzer. Turns out you can just look at the red label on the transponder. (look in the trunk, next to the spare!)

Fob Tx (from fob to car) is 312.15 MHz, FM. There's a lot of data in them packets too!

As for RF immunity... The fob seems to handle DCEP arc welding at 80-90A just fine. Note that the cable went right across the fob! And the welder was one of those nasty, high ripple pseudo DC inverters! I was actually worried about this, but it seemed to take it without any detrimental effects. Then again, this stuff _SHOULD_ work correctly....