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Ok,
So I actually looked up the components you'd need to do this.
Here's the first low power Bluetooth chip I came across... the FIRST:
https://www.csrsupport.com/dow...
It needs 16mA while transmitting.
1mA while idle
900nA while in sleep mode
The size is well with their specs.

The we have the harvester:
Again, the first IC I could find:
http://www.powercastco.com/PDF...

It's about 1/2" square, so it's a little big.
But it's already designed to power sensors.

The first chip already has a capacitor in it.
This even has use cases in the whitepaper describing something very close to what this kickstarter wants to do!
So the reciever charges the capacitor. When the capacitor gets enough charge to transmit, the Bluetooth chip does exactly that. So it's not a continuous connection. Based on the amount of RF in the area, it will transmit more or less often.
It appears, based on my back of an envelope math, it would have enough RF energy to operate continuously at at least 5meters from your typical Wifi AP or router. The further away you got, the fewer pings you'd get. But given our almost ubiquitous wifi coverage now, I'm pretty sure it would work.

Since your most likely device for connecting to it would be your cellphone, it's a pretty simple use case to say it would work like this:
You put the tag on your keys or cat
You install their "Find my tag" app
When you can't find the keys or cat, you open the app
The app TURNS ON the wifi in your phone, to power the tag.
You walk around looking, when you get near the tag, the wifi FROM YOUR PHONE will charge it.
All the tag does at that point is start beeping. That's it. You follow the sound.
The "I've lost you" signal is likely incredibly tiny.

This is all assuming they are even using the real Bluetooth standard. Who knows.
I do not know if this is a scam or not. It very well maybe. But the premise is entirely plausible if you just think about what they're really trying to do.

The eval board will turn any RF between 850Mhz and 950Mhz into DC power. Not a whole lot of it, but a useful amount for things like sensors.

See here for more details:
http://www.powercastco.com/products/development-kits/

See, this is what I mean by people just refuse to believe this technology is real. In that you're "skeptical", you think it's some sort of pseudoscience or something like that?

Is it me, or are people having a hard time believing the technology actually exists?

Two Companies Already Have Products:

http://www.powercastco.com/
http://www.witricity.com/

NY Times Covered this stuff in 2007

http://www.nytimes.com/2007/12/09/magazine/09wirelessenergy.html?_r=1&ref=magazine

Here's CNET demoing powercast's tech in 2007!
http://cnettv.cnet.com/powercast/9742-1_53-25606.html

You can buy full blown evaluation boards online that powercast manufactures that implement wireless electricity:

http://www.futureelectronics.com/en/technologies/development-tools/rf-wireless/Pages/9660812-P1110-EVB.aspx

Why is everyone having such a hard time with this concept?

http://www.powercastco.com/

Not magnetic induction charge plate based, actually over the air over medium distances, already here, products available for immediate delivery.... and nobody seems to cares. They've been around for a few years with shipping product and everything.

It's almost like people can't believe their product is real. It's so very strange.

Even won a best of CES in 2007: http://reviews.cnet.com/8301-12760_7-9673092-5.html?tag=ces2007;mcol

TRUE WIRELESS POWER
Powercast’s technology provides true wireless power for continuous charging and power-over-distance for one or more devices. Wireless power transmission is based on commonly used radio waves and Powercast's patented RF-to-DC conversion technology. The combination enables low-power electronic devices to become finally untethered with trickle-charge embedded wireless power.

Wireless Power Calculator
http://powercastco.com/wireless-power-calculator.xls
http://www.powercastco.com/resources/

Doing a simple calc with the above spreadsheet at 2.4 Ghz, 1W of radiated power, patch antenna, and five meters distance from the radiated power source, you would have just 0.040 mW of usable power, and at that, not enough to light even an average LED (30-150 mW req). So, don't be looking for that 'power on' indicator on this device. At that 'available power density' the charger might almost make up for its own internal losses from the battery charging circuitry.

For any device of this kind to be useful it needs to be broad spectrum and not limited to a single frequency band such as the 2.4Ghz band stated here. If you could capture all available RF in a large enough swath of spectrum then this bulky device might have enough power to be competitive with a teeny tiny button battery.

Wireless Power Calculator
http://powercastco.com/wireless-power-calculator.xls
http://www.powercastco.com/resources/

Doing a simple calc with the above spreadsheet at 2.4 Ghz, 1W of radiated power, patch antenna, and five meters distance from the radiated power source, you would have just 0.040 mW of usable power, and at that, not enough to light even an average LED (30-150 mW req). So, don't be looking for that 'power on' indicator on this device. At that 'available power density' the charger might almost make up for its own internal losses from the battery charging circuitry.

For any device of this kind to be useful it needs to be broad spectrum and not limited to a single frequency band such as the 2.4Ghz band stated here. If you could capture all available RF in a large enough swath of spectrum then this bulky device might have enough power to be competitive with a teeny tiny button battery.

• Radiative transfer: send a directed beam of energy from a source to a receiver. The advantage is that this can work over long distances, the disadvantage is that you need to either have fixed locations or some active tracking system to keep pointing at the receiver as it moves around, and you need some kind of automated kill switch to make sure you don't accidentally fry anything that walks between the transmitter and receiver or waste power when the receiver is not there. It looks like PowerCast and PowerBeam fall into this category.
• Traditional inductive, non-radiative power transfer. This works well, and does not transfer power when the receiver is absent, but is extremely short-range if you want any kind of efficiency; typically, the device to be charged must be sitting directly on or adjacent to the charger. The Wireless Power Consortium is pursuing this kind of approach.
• Resonant, non-radiative power transfer. This relies on the source and receiver being electrical resonators at the same frequency, so that they preferentially transfer energy to one another rather than to other objects in the environment via resonant coupling. This is the approach being pursued by WiTricity, where they additionally rely on resonators that couple primarily via magnetic fields (the electric-field energy is mostly in capacitors inside the devices), which have the advantage that most materials are non-magnetic at these frequencies so the power source dissipates very little energy into extraneous objects (or people). (In contrast, Tesla coils produce strong electric fields external to the device, which interact much more strongly with matter; it's no coincidence that Tesla coils are used as lightning generators.) This operates efficiently at mid-range distances although not as far as radiative transfer (meters at most), does not transfer or dissipate power when the receiver is absent, and is not directional so does not require active "pointing" of the power at the receiver. But it is more complicated than the short-range non-resonant inductive transfer, and requires careful impedance-matching of the source and receiver.

Full disclosure: I know Prof. Soljacic at MIT, who founded WiTricity, although I personally have no financial interest in the company; all of the above information is public and published, however.

For Powercast's technology, here's the spreadsheet that can be used to calculate transmission efficiency given distance, frequency, etc.
http://powercastco.com/wireless-power-calculator.xls

Here's a company that's had wireless power tech since 2007:
http://www.powercastco.com/
They even won a best of CES 2007 award from CNET:
http://reviews.cnet.com/8301-12760_7-9673092-5.html
They released working wirelessly powered Christmas tree lights in December 2007 as a consumer product!
http://news.cnet.com/8301-17938_105-9793204-1.html
So this type of wireless power tech has been available in consumer products since 2007 and it appears that there has not been a lot of interest. I am really mystified as why nobody cares. Is it because they mistake this technology for some other kind of well known technology? I can't figure out the psychology here.

These guys developed the same technology too. They have released commercial products, demoed and won awards at many trade expos and you can even order a developer kit:

http://www.powercastco.com/

It's amazing the amount of unfounded disbelief and misunderstanding of this technology on this thread.

http://www.powercastco.com/

True Wireless Power

Powercast recognizes there are several alternatives available for powering devices without the use of wires, each with different addressable markets. The alternative methods may seem similar on the surface, however, they offer limited solutions. Powercast is the only company with the technology and component-level products to deliver continuous charging, and provide its capability at a scalable distance.

They even won a best of CES 2007 award from CNET:

http://reviews.cnet.com/8301-12760_7-9673092-5.html

They released working wirelessly powered Christmas tree lights in December 2007 as a consumer product!

http://news.cnet.com/8301-17938_105-9793204-1.html

Stuff like this comes up all the time but disappears down the memory hole very shortly thereafter.

There is an American company, Powercast, which is claiming to already have FCC approval for wireless power transmission.

WPT series Powercaster(TM) modules are programmable frequency
sources for use in RF power harvesting applications. The modules
encapsulate proprietary algorithms which extend the effective
range of power transmission without increasing average power. Numerous
standard units are available, with customization available
upon request.
The WPT9066 module is optimized for operation in the 902-928MHz
ISM band. A highly accurate and stable oscillator centered at
905.8MHz is utilized to minimize wander, distortion, or other ill effects
that could cause interference with other devices. Custom frequency
ranges are available upon request.

Official webpage: http://www.powercastco.com/ Also, they were picked "Best Emerging Technology at CES 2007" Theres other links availible on their webpage (and from google), and NONE of the source articles are dated April 1st.

Write-up from Jan.

Official Site