A record 689,313 alerts were sent to users of the NHS COVID-19 app in England and Wales in a week, NHS figures show.
The alerts tell people they have been in close contact with someone who has tested positive for coronavirus.
The new number was recorded in the week up to 21 July.
The previous week's numbers showed 618,903 people were pinged by the app.
Businesses in all sectors have complained that they are struggling to maintain operations when so many staff have been told to stay at home to break the transmission.
The government has said that some essential workers can now use daily testing to avoid having to isolate.
The car industry has joined calls for the government to bring forward the date for exempting fully-vaccinated adults from self-isolation rules.
It comes after a slump in production blamed on the so-called "pingdemic".