Apps use push notifications to buzz users’ phones or tablets with updates on new messages or alerts. When a user enables push notifications, Apple and Google create a small bit of data, known as a token, that links their device to the account information they’ve given the companies, such as name and email address.

In his letter, Wyden said the federal government had started demanding records on those tokens from Apple and Google because those companies operate as a “digital post office” for relaying the notifications. The tokens could reveal details about who a person is communicating with over a messaging or gaming app, what times they talk and, in some cases, the text of any message displayed in the notification.

Depending on how users have set up their push notifications, the token data could also potentially expose limited information about anyone who had exchanged emails, texts or social media messages with someone that federal investigators have pursued.

Never use push notifications people.