Like wearing a mask, social distancing, washing hands and contact surfaces, the contact tracing app is only as useful as number of people who elect to use it.
In abnormal circumstances we have to sacrifice or surrender certain rights for the greater good as well as for our own protection. Seems like a small price to pay to install and switch on the app. You can switch it off after the pandemic ends. Unless of course you have an Android phone or any mobile device containing a Huawei chip or you've installed apps like FaceBook, certain browsers and Uncle Tom Cobley and all which already track you physical movements as well as your online activity. Allegedly.