The world's biggest high-tech fair opened Tuesday with IT giants aiming to bounce back strongly from a terrible 2009 by wooing consumers with trendy gadgets.

"Connected Worlds" is the theme of this year's CeBIT fair, with companies showcasing energy and labour-saving devices that use wireless technology to communicate with each other and with users far away.

But, as ever, the CeBIT is not all work and no play.

A host of futuristic devices were on display, from mobile phones that can open your front door to "silent sound" devices that measure the movements of your lips and transform them into sound.

And hot on the heels of the stunning success of James Cameron's 3D film adventure "Avatar," this year's CeBIT was definitely best viewed in three dimensions.

From screens that transform two-dimensional images into three by monitoring a viewer's eye patterns to 3D Internet that allows shoppers to "try on" the latest fashions, 3D is the show buzzword.

This year, however, the CeBIT takes place against a tricky backdrop for the high-tech sector, as the industry recovers gingerly from a crisis 2009 and cautiously eyes better days ahead.

According to German IT industry lobby, BITKOM, turnover in the sector will be flat this year, before growing by around 1.6 percent in 2011 to 142 billion euros (193 billion dollars).

After a catastrophic 2009, where turnover shrank 4.3 percent, "demand is taking off significantly, especially in the IT sector," said BITKOM President August-Wilhelm Scheer.

The CeBIT fair itself has also seen better days. This year, fewer than 4,200 companies are at the event, in Hanover, northern Germany. This is around half the number attending in the halcyon days of the dotcom boom.

But opening the fair, Chancellor Angela Merkel and Spain's Prime Minister Jose Luis Rodriguez Zapatero both stressed the importance of the sector for Europe.

"The future of Europe is digital," said Zapatero, whose country is the partner country for this year's CeBIT.

Surrounded by around 200 journalists and officials, Zapatero and Merkel visited some of the more high profile stands, such as IBM, Microsoft and Telefonica, during a traditional opening day "walkabout".

Despite the crisis, the digital sector in Germany still enjoys a captive audience.

A survey published Tuesday in the Die Welt daily showed that 93 percent of Germans aged 20-24 are members of social networking sites like Facebook -- "what's wrong with the other seven percent. Are they living in a wood?" the paper commented.

A BITKOM poll showed that nearly one in four Germans would be prepared to have a microchip implanted into their body if they thought they would derive concrete benefits from it.

But not everyone is convinced, however, by the relentless march of technology.

"Machines were invented primarily to make life easier. Since that time, they have overtaken our everyday lives more than we should be happy with," wrote the Berliner Zeitung in an editorial.

"The time that we save by checking on our smartphones when the next bus leaves is wasted by double and triple-checking the Facebook status of people we have met maybe twice."

The CeBIT wraps up March 6.