First, they set about persuading housewives to have a team of five or six men rummaging through their homes recording all of the household products they used, then persuading suburban householders to put a large and intrusive sign in their front yard.

More on that later, but it's a technique that has perhaps its most insidious and game-changing use today in election campaigns – and will play a part in the ACT's election for the first time this year.

That is thanks to Alex White, who lacks nothing if not chutzpah, a young man who plays the insider style of politics, a game of numbers. The boss of Unions ACT, White comes to Canberra fresh from Victorian election campaigns where they play politics hard.

In 2014, White volunteered with the Victorian Trades Hall Council, knocking on hundreds of doors during the state election, with a paramedic, a nurse or a firefighter by his side. Once inside – and, as he cheerily points out, people don't close the door on an emergency services worker – White and his co-volunteer finish their chats with swinging voters by asking them to sign and date a pledge.

The wording is innocuous enough, with the pledge simply asking voters to sign off on their commitment to quality schools, well-funded public hospitals, emergency services and they like. Then they're asked to go a step further and finish the statement "This is important to me because …" before signing and dating the pledge.

The union team keeps the pledge, and then crucially, a couple of weeks before election day, the pledge is mailed back. In this way, voters are reminded of what they signed up to – in their own handwriting and their own words - as they head off to vote. They also receive a "report card" on where the major parties stack up in relation to their pledge, so they're left in no doubt of where their vote must go if they are to keep their promise, a promise to the union and to themselves.

In Victoria, the union campaign handed out how to vote cards that put the Liberals last, and Trades Hall Council secretary Luke Hilakari says scrutineers reported that 16 per cent did just that. Exit polling showed that of people who voted "progressive" (Labor, Greens, Sex Party), the No 1 issue was emergency services, not an issue people would usually nominate as their No 1 concern without the messaging that had come before. The next most cited issue was education, then jobs and health, a clear indication the union messages had been heard. Post-election polling in four of the marginal seats targeted by the unions showed that of those who had had contact with the union campaign, more than half, 54 per cent, had voted "progressive". Among people who hadn't had contact with the union campaign, 51 per cent voted Liberal.

This is all the proof that Hilakari needs that the technique works. He dismisses suggestions that there is anything manipulative about it, saying the campaign is all about authenticity – real conversations with real workers – and helping people feel part of a movement. As well as conversations and pledges, his doorknockers offered people selfies with the workers on their doorsteps which were then shared on social media. Thousands took up the offer, he says. A bit of fun, a sense of connectedness, ordinary people getting fired up about being part of democracy and believing their votes matter.

Hilakari has had plenty of experience of the other side of political doorknocking, where no one wants to know you. But turn up with an emergency services worker or other frontline worker and "it's chalk and cheese".

"Your typical door-open rate might be one in five, maybe one in four depending on the weather but if you're knocking with genuine purpose the doors always remain open and people want to engage in that conversation, it's totally different."

The 1966 "foot in the door" research was based on the idea that once you agree to something small, you're more likely to agree to something big. When the women were asked straight out whether they would agree to have five or six men come into their home for two hours to classify all of their household products, with full freedom to rummage around and search cupboards, only 22 per cent agreed. But if they had agreed to a small request first, the numbers surged. Among women who had first taken part in a telephone survey on their use of household soaps, 53 per cent agreed to the big request – the invasive household audit.

In a second experiment, the researchers asked to put up a small sign, just three inches square, in their window or car saying "be a safe driver", or "Keep California beautiful". The second, much bigger request two weeks later was to install a very large sign in their front yards, saying "Drive Carefully". The sign that would obscure the driveway and much of the front of the house. Again, while fewer than 20 per cent agreed without the preconditioning, more than 55 per cent agreed if they had already agreed to the petition or small sign.

The researchers put people's willingness to comply with big requests down to a change in the way they see themselves. They become, in their own eyes, "the kind of person who does this sort of thing, who agrees to requests made by strangers, who takes action on things he believes in, who cooperates with good causes".

And so with the union pledges, the voter becomes the kind of person who believes in public hospitals, or funding for emergency services, or quality education. And later they are told, with the helpful return calls and report card from the unions, how to give effect to that perception of themselves: put the Liberals last.

Pledges are used more by the left of politics than the right, and are put to use in Barack Obama's campaigns. They were also at the heart of the Rock the Vote campaign during the 1996 US presidential election, aimed at getting youth to vote. People were asked to fill out pledges which were mailed back a fortnight before election day. The campaign issued two pledges – in a second version, the young people were asked to complete a sentence that began "I will vote because ...".

A study by Minnesota researchers of the impact showed that people who received one of the pledge cards containing the "I will vote because" prompt were significantly more likely to vote (83 per cent voted) than those whose pledge cards didn't include the prompt (70 per cent). Intriguingly, the effect remained even when voters hadn't actually filled the prompt out – just having it there made them more likely to comply. The researchers pointed to a series of studies showing that making a written commitment to do something significantly increases the chance you will do it – from wearing a seatbelt or safety glasses, or recycling.

But it's not only about the written commitment – with research showing that even simply being asked in a phone survey to predict whether you will vote in an election increases the chances that you will. The researchers speculated that cognitive dissonance theory plays a part, with people avoiding inconsistency between their "desired self-view" and their behaviour. Simply asked to "generate meaningful reasons" for a behaviour increases the chances of carrying it out.

Dr Andrew Hughes from the Australian National University's research school of management says the pledge moves people from being uncommitted to being committed. Once you have persuaded someone to sign a pledge, you have already changed their behaviour – and by signing it, by taking a tangible action, the voter has solidified and cemented their behaviour.

He compares it to putting down a deposit on a movie ticket for the weekend – it's not the size of the deposit that matters, it's the tangible action that makes it more likely you will follow through.

It also taps into the social movement aspect of politics, helping people feel engaged and part of a movement, adding excitement and "making it come to life".

And as Hughes points out, it's not a difficult commitment – you're committing only to a single vote at the coming election. It's easier than agreeing to attend meetings, wear the T-shirt, volunteer time or even than joining a club. It's a short-term commitment that doesn't clutter your life. You think "I can just do this, it takes a few seconds, it adds value to my life then I move on with my life".

Hughes said the pledge campaign "is really targeted at people whose engagement levels may not be as high as others", allowing them to sign up to an idea without having to be closely involved in the detail of an election campaign or policies. He points to Donald Trump's appeal, which works on that level – supporting Trump doesn't mean committing yourself to anything more than Trump, to a broad movement.

The unions are also tapping into what's called "authentic branding", using ordinary people rather than apparatchiks to endorse a political brand, especially valuable at a time when politicians' credibility among voters is so low. The campaign gives a sense that there's momentum behind a campaign.

"Momentum is a very important in politics. Who wants to be part of a winning team? Everyone. No one wants to be part of a losing team," Hughes says. "If you've got [momentum], people come towards it, it's like a magnet."

Alex White has the ACT election all worked out. Canberra has five electorates. Each will elect five politicians – most likely two Labor and two Liberal in each, with the fifth seat in each electorate up for grabs. White is ignoring the central electorate where the Greens' Shane Rattenbury holds the fifth seat and is expected to win it again. A seat for the Greens is one for Labor, in effect, so the hard work is already done there.

White is targeting the other four electorates – Tuggeranong, Woden-Weston, Belconnen and Gungahlin. Labor (or the Greens) needs to win the final seat in at least two of those electorates to keep government (giving Labor 12 seats across the five electorates (3, 3, 2, 2, 2) and the winning one to the Greens).

White has already identified 8000 voters across those four electorates that he will target, his "We Are Union" doorknocking and pledge-signing starting tomorrow. They have been identified through polling, robocalling and surveying to establish their voting bent, with the campaign targeting those regarded as "persuadable", as well as some firm Labor and Greens supporters to ensure their vote stays put. White believes he only has to turn 400 votes in each electorate to ensure that fifth seat goes to Labor (or "progressive", since he denies backing any one party and insists that the influence of his campaign will see Labor commit to some of the union agenda, not the other way round). The 400-vote calculation is based on the way votes are counted - candidates with the lowest primary vote are progressively eliminated and their preferences shared among those left in the race, so it becomes crucial to get sufficient primary votes to stay in the count and gather preferences from others - to "survive the hunger games", as it puts it..

White says the campaign technique is the reason Liberal governments were dumped in Victoria and Queensland in the past 18 months after just one term, and he is supremely confident it will work here as well.

"We'll change the outcome of the election, our campaign will change the outcome of who is elected in all four electorates that we've targeted," he said.

White says doorknocking is a waste of time for politicians – not only are they held in low regard, they also waste time knocking on doors of people already rusted on to one party or the other. And most people won't open the door. But when there's an ordinary worker at the front door, it's a different story. Paramedics, fire fighters, nurses and others can't wear work uniforms for doorknocking, but will wear clothes that clearly and immediately identify them as a firefighter or nurse – high-visibility gear, scrubs, T-shirts.

"When I did it [in Victoria], and I knocked on hundreds of doors, everyone opened the door," White says. "If there's a firefighter coming up the drive people are interested. It's not union officials going and talking."

While he insists pledges change votes, he rejects suggestions that they are manipulative or unfair.

"We're not telling people how to vote and we're not forcing them to sign a pledge, we're having a conversation where they've said they deeply care about healthcare and they've got a nurse talking to them about healthcare, and then at the end of it we ask them to sign a pledge saying they care about healthcare ...

"We know that when we ask people to a sign pledge about issues that are important to them they're more likely to act on that. But it's something they choose to do ...

"The other thing we're doing is being completely open and honest about who we are. We're wearing T-shirts saying we are union we're only talking to union members and union supporters. We're completely open and transparent about what we're doing, who we're talking to and who we are."

Hilakari says Alex White was "terrific" in the Victorian campaign. "He understood it immediately," Hilakari says. "I wish him and all the comrades up there the very best for the coming election."

White denies his campaign is about keeping the Labor Party in power – he says it's about changing the policies and promises of both major parties - but it's a denial safely ignored. He and his volunteers will be doing everything they can to ensure Jeremy Hanson's Liberal Party is defeated. If Labor scrapes back it will be difficult to assess the contribution of White's campaign. But if Labor wins that prized third seat in three or even four electorates, an outcome that looks at this point firmly beyond its reach, Labor leader Andrew Barr might well have to acknowledge Alex White his kingmaker.