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I've had my Prius less than two weeks, but I had read the manuals a few times while waiting, and enjoyed this forum and others. I thought I would be able to handle most questions thrown at me during a demo.

Right off I showed the car to an engineer. So, Okay, I'm stumped.

His question concerned Smart Key System operation while the fob is IN the car. I had no problem explaining that OUTside the car, the fob will get out of range eventually and the activity is over for the car and the fob.

But he asked if it were any easier (on the fob) for the Smart Key to actually be inserted. His question was, wouldn't it run down the fob's battery for it to be telling the car "I'm still nearby"?

I wanted to answer, "I don't think the car cares about the fob once the car starts, so the fob battery doesn't get a workout." But is that right?

To avoid confusion, "Smart Key" is equivalent to "fob" in the above.
 

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Well, if the fob is like other Radio Frequency ID's, then it is powered by the host device or reader. The radio waves transmitted by the host are actually used as the energy needed by the fob.

Oddly enough, Tesla, the famous electrical genius, wanted to transmit power to homes this way.
 

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Power to the people

That explains why I pay Edison each month and not Tesla. :lol: Though I'm sure with a better agent he could have figured out a way to charge for it. We certainly collect tolls and transit fares just that way.

Thanks for your reply. It was very engineer-worthy and will help.
 

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Ok, I looked this up in the technical manuals.

When you press the "POWER" button in the Prius the 'room oscillator' turns on seeking the transmitter (your fob). Once the signal hits the transmitter the transmitter/fob transmits it's security code back to the Prius.

This is a one time transmission and thus only one brief drain on the transmitter/fob.

If a transmitter/fob is within range of the 'door oscillators it's a different scenario. Where the 'room oscillator' shuts off once it recieves the code from the fob, the 'door oscillators' remain on continuously while the doors are locked. Once unlocked it'll stop sensing. Thus, if the fob is in range of the active door oscillator and remains there it will continuously transmit the security code data until the battery drains or the door is unlocked and thus can drain the fob battery much more quickly than otherwise.

A small aside. The door oscillator sensing frequency can be changed from the default 300hz to 150 or 900. That's the number of times per minute it sends out a code looking for your smart key fob. The higher the rate the faster it drains you 12v battery. Thus, again, why you should turn off the SKS when you'll be away from your car....now, however, I wonder if it matters if you're leaving your car unlocked if it makes any difference since the door oscillators should be off if the doors are unlocked.

Another aside. The hatch oscillator is only activated by depressing the button in the handle on the hatch.
 

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efusco said:
Ok, I looked this up in the technical manuals.

When you press the "POWER" button in the Prius the 'room oscillator' turns on seeking the transmitter (your fob). Once the signal hits the transmitter the transmitter/fob transmits it's security code back to the Prius.

This is a one time transmission and thus only one brief drain on the transmitter/fob.
That explains why you can remove the fob after starting the car and the car still runs.

efusco said:
....A small aside. The door oscillator sensing frequency can be changed from the default 300hz to 150 or 900. That's the number of times per minute it sends out a code looking for your smart key fob. The higher the rate the faster it drains you 12v battery. Thus, again, why you should turn off the SKS when you'll be away from your car....now, however, I wonder if it matters if you're leaving your car unlocked if it makes any difference since the door oscillators should be off if the doors are unlocked.
To Quote Toyota "Transmit Interval - Function to set the smart key signal interval transmitted from the outside of the vehicle when the vehicle is parked"

This means the "Transmit Interval" (150, 300, 450, or 600ms) is not how many times/second it looks, but the time between looking. The default of 300ms means look every 300ms for a fob. I am considering increasing this to 600ms to reduce the number of times/second the car looks for the fob and thus decrease the power consumption from the 12v system.
 
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