Prime Minister Scott Morrison rang alarm bells Friday morning when he refused to "be drawn" into commenting on whether the Government would consider making its planned contact tracing app “compulsory” if voluntary take-up fell short.

Speaking on Triple M Hobart radio, Morrison was pressed on the Government’s plans for getting the app onto people’s phones.

“For this to work, we need a lot of people to download this app,” he said.

“Now, in Australia, my preference - my very strong preference - is that we do it this way, with Australians [downloading] it by permission.

“If we get good coverage of people doing that, this is really going to help.”

Morrison said that Australia would need “at least double” the reported 20 percent voluntary take-up rate of the TraceTogether app in Singapore.

Asked whether the Government would make the app mandatory, requiring Australians to have it active and on their person at all times, Morrison said: “My preference is not to do that. My preference is to give Australians the go at getting it right.”

Pressed again on whether mandatory measures would be considered, Morrison responded: “Oh look, I don't want to be drawn on that.”

“I want to give Australians the opportunity to get it right. That's my objective, that's my plan A, and I really want Plan A to work.

“I'll be calling on Australians to do it frankly as a matter of national service. In the same way people used to buy war bonds back in the war times, to come together to support the effort.

“I know this would be something they mightn't normally do at an ordinary time but this is not an ordinary time, and if you download this app, you'll be helping save someone else's life. I think Australians will respond to that.”

Morrison also said a high use of the app would likely lead to a loosening of current restrictions.

“Here's the simple deal - if people download the app, and more people have got it, the more soon we can start easing off on some of these restrictions,” Morrison said.

Software engineer Dan Nolan said in a Medium post overnight that getting enough people using whatever contact tracing solution is proposed will be the big challenge.

“Getting someone to install mobile apps is extremely hard,” Nolan wrote.

“As someone who has made their living for years on selling or getting people to install apps it’s a complete nightmare.

“App installation trends have been consistently going down over the past few years, getting people to install an app to solve this problem is never going to work.”

In that way, contact tracing capabilities built directly into mobile operating systems - something Google and Apple are working on - is likely to be a more reliable path to higher take-up.

However, Nolan noted there were key technical and usage concerns that would still need to be addressed.

“We need to be very clear in terms of what these systems collect and how,” he wrote.

“Any murkiness or lack of clarity will defeat the project before we start.

“If people are sceptical because of poor communication from the government or tech vendors the entire project will fail.”