An app update rolled out at the weekend allows TraceTogether to run in the background on iPhones to exchange Bluetooth "handshakes" with nearby devices for contact tracing.

Previously, the app had to run in the foreground, which drained the battery and meant users could not use their handsets for anything else.

Android devices do not face the same issue.

On the TraceTogether website, the app's creators from GovTech said all that users need to do now is to turn on their phones' Bluetooth and keep the app open in the background.

Battery drain was the biggest issue for freelance graphic designer Shamsul Othman, 29, before this app update. "I felt that running TraceTogether actively was draining my battery and, more importantly, I would not be able to text or use my social media apps if I had to keep it running all the time," he said.

But the problem has now been solved, after the GovTech team tweaked the app, allowing it to work while running in the background.

Even so, two iPhones with TraceTogether running in the background are still unable to exchange signals, due to Apple's settings that prohibit the apps on both phones from communicating with each other while being used in the background.

This means TraceTogether covers only three-quarters of all encounters of the more than 2.1 million handsets with the app.

The GovTech developers said they are still working to improve the app.

The agency did not adopt tech giants Apple and Google's Exposure Notification system - rolled out in mid-May for privacy-preserving contact tracing purposes - as the system was said to be ineffective.

Specifically, contact tracers using the Apple-Google system will not be able to map out the chain of infection, which is critical for epidemiological investigations and to identify clusters. What they will get is a pool of infected persons and a pool of close contacts, with no way of linking individuals.

Instead of working with Apple and Google, Singapore has started making a small gadget, dubbed the TraceTogether Token, to improve participation for digital contact tracing. Even people without a phone or a new smartphone can be included.

Vulnerable seniors - such as those living on their own, have poor family support or are physically frail and do not own or use digital devices - have started receiving TraceTogether tokens.

Locally based electronics firm PCI won a $6 million tender to supply the first 300,000 TraceTogether tokens.