Is ambient activity a way to grab column inches? Or do new tools for measurement and accountability help to make it a more serious proposition?

You can pin an ad on someone's forehead, but can you check it, track it and research to see if it does an effective sales job? Although ambient media covers a whole array of out-of-home opportunities to see, hear, smell and sample that might seem hard to pin down, there is a drive to make it more accountable.

The presence in the ambient media marketplace of big media owners such as Clear Channel and Viacom and an increasing number of blue-chip clients has helped to bring research and accountability higher up the agenda.

There's more money to invest in bespoke and industry-wide initiatives and there's a desire to give scientific backing to media that have still got a bit of the "did I hear you right?" feel to them.

One could argue that some of the media formerly known as ambient have arrived in the mainstream precisely because they have a serious degree of accountability. At the outdoor specialist Concord, the chief executive, Nigel Mansell, says there are aspects of ambient that are moving into the mainstream. He cites trolley and washroom advertising. Both can offer national coverage and both have a concrete way of measuring effectiveness in the form of electronic point-of-sale data from the tills of the supermarkets and motorway service stations where they appear.

The other "ambient" players that are aiming to enter into the mainstream are the transport media. By the start of 2004, the outdoor media industry research system Postar plans to include a pedestrian research model as well as its original roadside model. This means that it would include advertising on underground and buses as well as rail and taxis. It seems that Postar is keen to include any ad going past you or any which you go past.

Stevie Spring, the chief executive of Clear Channel UK, which includes in its portfolio plenty of special poster sites, as well as Taxi Media and a holding in The Media Vehicle, is one of those who thinks that some forms of ambient tick all her boxes for inclusion in the mainstream. "They are robust, well-researched, replicable, actionable and campaignable," she says.

At Taxi Media it's clear how important accountability is to both Clear Channel and its clients. Lloyd Keisner, the sales director, describes how the company now has two systems to keep tabs on performance - both introduced since becoming part of a big media owner. "We have developed a model to evaluate the likelihood of encountering a taxi ad in all the major cities. It's probably the only coverage and frequency model for taxi advertising. And we launched 'taxiweb' last October, which is an internet-based posting verification system." Every taxi ad has its picture taken and slapped on the site so that conscientious marketing managers can keep a check.

At Viacom Outdoor, research is seen as part of the furniture. It already conducts regular research for its bus ads, talking to 300 people every two weeks. The planning and insight manager at Viacom Outdoor, Steve Cox, says that almost all campaigns come with research as part of the package.

Admedia specialises in washroom sites; over eight years it has built up a consistent national offering. "From the start we had a different, corporate, professional training and we identified that accountability was important," the chief executive, Philip Vecht, says. Having sites across motorway service stations means it can monitor sales through the EPOS data from the tills. So, when it ran a campaign for Lucozade Solstice, it was able to see a 500 per cent increase in sales. Vecht explains that he has three core methods of research: independent, tailor-made market research; measuring sales uplift, and direct response. And if his clients want to be sure that the ad has gone up in the first place, he has a team of in-house vans to do the posting.

Another of Admedia's areas of interest is sampling, which is perhaps more in the heartland of true "ambient" media. It recently sent 250,000 samples of Listerine oral care strips into the community, targeting young trendsetters. "More theatre than distribution", is how Vecht describes the campaign. Although conventional research was problematic, the client wanted to see results. The answer? The client literally turned the camera on the agency and filmed Admedia's team at work creating that all-important buzz factor.

To many, ambient media is all about creating buzz. It's the sort of advertising that is very difficult and perhaps artificial to measure. At Diabolical Liberties, the run-of-the-mill includes a recent headline-grabbing placard at the anti-war march in London, which carried the message: "Make Tea not War." The company's team of foot soldiers are up for spreading the weird and wacky word of advertisers on to the streets and into the cooler clubs about town.

The new-business director at Diabolical Liberties, Maryanne McNamara, is certainly up for a bit of accountability. "We are interested in accountability because our clients are interested in having as much information as possible," she says. "But with some things it's more appropriate, other activity is more difficult." The company did its own recognition and recall research after a guerilla marketing campaign for Calvin Klein, which gave them an impressive figure of 70 per cent recognition among a leading- edge audience.

A lot of the underground activity which companies such as Diabolical Liberties or its competitor Cunning Stunts are involved in defies conventional measurement. A clipboard and pen would seem a bit out of place in a sweaty nightclub. Instead, such outfits rely heavily on feedback from networks of opinion formers - both in-house and independent.

Cunning Stunts is behind the recent initiative to brand students' foreheads with advertising messages. So, how do you measure that? "There are rules of getting out and about and they are taking photos in sites," Cunning Stunts' strategic director, Janine Abrahams, says. And then there are column inches; clever stunts invariably get good - and measurable - PR.

But you get the feeling that despite some thoroughly useful feedback, much of ambient comes under the heading "90 per cent trust" or "the icing on the cake". This means that from the client end, the serious research is more likely to concern other media for the time being.