have a look in the search section. there has been several discussions about shark shields over the time.

with a rescue diver who reckons that all the pro divers got em and not NONE of em use them anymore.
reckons something along the lines of
'they replicate teh heartbeat of a larger shark, hence scaring off the smaller one. but what if you have a 5m white heartbeat and a 6m comes along?' interesting. anyways he reckons that these guys all find more sharks when they wear em, and that it actually attracts them from a distance and repels in close quarters.

this also from a mate recently - i had a laugh.
http://broceanography.com/2008/03/04/shark-eats-anti-shark-device/

don't mean to badmouth them - i haven't made up my mind yet, just these are the last 2 things i've heard of the devices.

I give the story about them replicating the heartbeat of another shark about as much credence as I would tales of women riding around the night on broomsticks, its from exactly the same basket.

You can read about how they actually work here; <click>

The one that got bitten was apparently malfunctioning, pretty embarassing in any case.

Tomo ...I bought a couple about two years back and as far as I know  they haven't been tested .......I'm happy with that .

What I can say is that it does give you a degree of comfort ,knowing that your wearing one .......so when those big school of buff bream cast a big shadow over the top of you at rottnest ...well lets just say I only have to lighty rinse the wet suit.

the boat that i went with was involved in the testing of them and they swear by them,

good enough for me to go and buy one the very next day.....not that i bother to use it very often but i do believe they work.

Sort of becomes like a seat belt where you feel funny when it is not on.

You forget that you are wearing one until you get in a tight spot and it comes back around and gives you a buzz...I hate that. You also have to be careful of people around you. Quite often you can give them a tickle as well if they swim under you.

I did read a coroners report though from a scallop diver in South Australia who was killed with one on...not great...but from memory it was concluded that though the device was on, and working, the diver had turned it off when on the bottom....Which makes sense (from my experience) as the tail of the shield can get you. They say to be effective it must be left on!!

The link to the report follow.

http://www.courts.sa.gov.au/courts/coroner/findings/findings_2003/buckland.finding.htm

In looking for that report I found plenty of information on the net about shark shields. It seems that the scallop diver is not the only fatality whilst wearing a shield!!

My conclusion: they are an incremental safety device. They can get in the way when chasing crays on the bottom so you do tend to temporarily turn them off...which apparently is a no-no. I think if a shark was a bit inquisitive they would save your life and they would deter small sharks from coming too close....but if a great white zoned in on you from 100 feet and came charging...you would be mince meat before the shark felt the small electric charge.

I hope that helps. I will still wear mine.

get a speargun instead. a good one can be cheaper than a shark sheild, and you can grab a few fish on the way!! it definately makes me feel a fair bit safer!!

seriously though, me and a mate had to fend of a BIG bronzy (seriously close to 4m) about a month ago up north. a couple of good hard pokes with mr rob allen, and he was history. its good to know that even if that didnt deter him, cutting the cord and pulling the trigger, and sending a 2m spear into his eyes or gills would have made him understand. sounds a bit brutal i know, but if it comes down to him killing me, or me killing him, i know what i would rather prefer.

A couple of years back I was on the boat recovering the bodies of those killed in the boat/barge collision off Carnarvon. Even before the three police divers entered the water they had been warned that there was two sharks over 10 feet and another two about 8 feet long circling the wreck site on the bottom. They had no problems at all from the sharks while doing the recovery thanks to their shark shields even with blood  and body fluids being present in the water.

Speaking to them after they said they would not have gone in the water with out them knowing that the big sharks were there but had no hesitation with the shields.

like anything there are freakish Sharks that dont fear the shield, like sometimes someone gets tazered and it doesnt really affect them or pepper spray being spray on someone just gets them angrier just a thought.

As far as divers and sharks go .......its the spearfishers that seem to have the majority of the shark encounters .

So the old saying " you won't see the one that gets you " is pretty much on the mark ! 

Does the mob that manufactures these things offer any kind of compensation if someone gets attacked while wearing one? Or are there too many variables...species of shark, temp and/or salinity of water, visibility, mistreatment of device, failure to operate device properly, etc etc etc?

Kept the 2.1m bronze whaler at bay while at the abrolhos this year, they work a treat!