The hot, new, must-have item in Japan is not the latest smartphone or computer pad, but a geiger counter - a device that measures radiation.

After the operator of the Fukushima nuclear plant this week confirmed meltdowns in three of the facility's reactors, geiger counters have sold out in most electronics shops.

"Before, no-one even looked at geiger counters or knew the name of them," electronics store manager Makoto Ogasawara said.

"But ever since the massive earthquake struck, people have become very interested in them. So we are selling 100 times more geiger counters than before."

The reason for this surge in sales is simple - good old-fashioned scepticism, even cynicism, directed at Japanese authorities and the operators of the Fukushima plant.

Many people simply do not believe the information that is being released, while others say the extent of the disaster at Fukushima is being covered up.

Another cause for concern is that radioactive traces above safety standards have been detected in crops grown well away from Fukushima - for example, a tea plantation even further south from the plant than Tokyo.

"I don't think that the information you got of the real information in Japan that is the problem," said Bruno Menard, a French chef living in the capital.

"I mean, I checked this morning, a French company in French, there was some warning that the level is very high around Fukushima and especially when it is raining, we have to be concerned."

Mr Menard has much to be concerned about. Rain is predicted for the rest of the week in Tokyo and the shops are sold out of geiger counters.

Manufacturers of these gadgets, like Japan's Fuji Electric, are among the very few industries to benefit financially from this nuclear disaster.

Its factory is working around the clock to meet the soaring demand.

"We are producing four to five times the number of geiger counters than before," Fuji Electric chief executive Michihiro Kitazawa said.

"We have also been producing devices that are easier for people to operate."

The factory produces about 2,000 geiger counters every month.

Right now that is nowhere near enough to keep up with demand - the ABC's Tokyo office ordered one weeks ago and has been told it will not arrive until well into next month.