There seems to be some confusion about the Google and Apple Covid-19 API.
It only uses bluetooth, it generates random ids every few mins, the contacts (random ids) are only stored on the phone. After 14 days the phone deletes the details. At no point is any contact information sent or analysed centrally. If you report as having covid-19 then your random ids in the preceding periods are sent centrally. Then other phones can download that information and check against their list of contact random ids. At no point will the other users know it was you, unless you tell them, or they are fairly close friends and would know anyway. It does not need location turned on, nor does it need it.
Bluetooth is very low energy, and that is one thing I do leave turned on, on the phone.
But the technology is not on old Android and IOS phones so I bet a fair percentage of population cant use it anyway. Which begs the question how high a take up can it actually get, even if we are all willing to install an app?