Algi, it is the C1 version and it does not work. The ebay listing I bought mine on stated for Pentax in the title. The C1, C2 etc is only a different connecting cord, the unit is the same. I have email confirmation from Yongnuo stating they made a mistake, it is not compatible and I can return it for a refund if I want.
Can't now find the linf but on one of the flickr discussion groups they also stated it does not work.
Algi, if you still dont believe me I will do you a good deal and you can try it for yourself

Does have wake up function but cannot be that alone as it would still fire when the flash was on. The pixel Soldier is working flawlessly at 1/180th so that does it for me. Might try and swap my business partner his pixel soldier for my YN-603, I feel it is the best solution for the business

SHOUL, but it does not work. They are now transcievers and have obviously upped the spec with some embedded code on a ROM to do some extra checks, hence it simply will not fire if the other wire is not connected. That's progress for you !

Algi, there is no reason why they should not work but I cannot get them to work ! I actually got an email from the seller this morning that confirmed although they sold them as "for Pentax", they will not work with Pentax. Looks like they are reading the other wire before firing, other wire is not making contact on Pentax so no fire. No easy way to fool it though as the "D2" wire on the Canon is producing a five volt sine wave a few microseconds before the flash is activated. It was a punt at £27, will be able to sell them to a Canon owner. They actually are a pretty good wireless remote and not that expensive if only used for this but I really need less things in the kit bag, not more ! The pixel soldiers are looking much better for me and also do the wireless remote bit, the CR2032 and AAA batteries are a pain as that is another two types of batteries to lug around, but other than that they are pretty good.

of course, cheers

Update on the Yongnuo RF-603 trigger (Canon model). They do not work with Pentax at all. Even removing the control wire, they do not work. They only work a a wireless remote. Also be wary of sellers on eBay, these were advertised as Pentax version, there is no Pentax version, only Canon and Nikon.
Pixel soldier, Canon version - work perfectly. CR2032 battery in transmitter, AAA batteries in reciever. 4 Group settings. Very secure hotshoe connections, lock and locking pin on the transmitter. Only have Kx on me at the moment so could only test wireless flash down to 1/160th but synching perfectly at 1/160th (Kx jumps from 1/160th to 1/200th and camera will not fire flash at 1/200th, very annoying as I wanted to see how much shutter was caught). The reciever can be used on the camera hotshoe as a wireless remote and the same 2.5mm phono controls the wireless remote and the studio light. Link to this one here
Can be bought in the UK for under £50. Just ordered mine
Anyone want a Canon trigger

PW II plus only requires 3 but older versions will be 4.
I am now becoming a wireless trigger boffin, even have a "decision matrix" for six brands. There is even a distant spark of an idea in the back of my head that I will use my 20 odd years in electronics manufacturing to make my own "ultimate trigger". So far, all triggers seem to have there failings, if I designed a unit that could do everything good from all the different current triggers I reckon it could sell quite well. Just a pipe dream at the moment but I do have electronic manufacturing contacts in very large far east companies. What would be the wish list :-
1) support all platforms - not going to be possible so platform specific, lets concentrate on Pentax for now !
2) Transceivers that can transmit and recieve at same time
3) hotshoe with lock and lock pin
4) AAA or AA batteries
5) Range 100m +
6) Grouping
7) "passthrough" hotshoe with P-TTL
Remote shutter release with half press autofocus
9) Standard 3.5mm phono connection
10) Selectable channels
11) Half press LED confirmation on recievers for grouping
12) Intervalometer
13) change speedlight "group" power from transmitter
14) Achieve full 1/180 sec sync

If this could all be done with a retai price under £100 ???
Anything missing from the list ?

Sorry for the tangent !

According to the Englinese manual it is an option. Would rather pay £2 exra to have it supplied ! Really like the pixel soldier doing it all with one lead, quite clever. The amount of leads and different batteries I am now carrying is not funny ! Should work witht he flash off camera without this lead so I can check the sync speed tonight.

The shutter release is a 2.5mm phono jack female on the side of the YN603 transceiver which goes to the 2.5mm phono jack plug female on the K20D body for remote shutter release. There is a cable supplied for this. This connection does not trigger the studio lights. There is a second connection on the front of the YN603 transceiver that is a PC female type connector which I believe is the connection to be plugged in to the studio lights. No cable was supplied for this. As our studio lights (portalight) require a 2.5mm phono cable male I either need a phono to PC adaptor to use the supplied cable or I need a 2.5mm phono to PC cable.
My confusion came as my partners pixel soldier trigger has only one connection that does both the remote shutter and studio light trigger. Should get hold of these tommorrow and see if they work on the K20D. Off to amazon to find my cable ...

I thought my partner was using RF602 triggers but it turns out his are pixel soldier (nice little triggers, will try his cCanon version on my Pentax). On his pixel soldier, the reciever has one 2.5mm jack plug connection, this works for both wireless remote (plugging it into the camera body) and triggering the portaflash lights (which also has a reciever 2.5mm phono jack plug). On the RF603 (and most likely the RF602 reciever), there is both a 2.5mm jack plug on teh side and a PC connection at the front. I tried the 2.5mm connection at teh side into the portaflash last night and got nothing, but it worked as a wireless remote using the same connection into the camera body. Wondered if I HAVE to use the front mounted PC connector to trigger the portaflash lights or if it simply does not work with Pentax ...