Twenty-one months ago, I installed the Virginia Department of Health’s COVIDWISE app on my smartphone and urged everybody reading that post in Virginia to go and do likewise. Back in August of 2020, I expected that this app developed with the Apple-Google COVID-19 exposure notifications framework would soon be warning me that I’d been near somebody else who had tested positive and had then used this app or another built on that foundation to send a thoroughly anonymized warning.

But the notifications of possible exposures didn’t appear, even as the U.S. suffered repeated waves of novel-coronavirus variants and the positive-test rate in Northern Virginia shot up above 30 percent at the start of this year. And as I got my first vaccination, second vaccination and booster shot, the continued silence of this app bothered me less and less–to the point that I briefly forgot to activate it after moving from my Pixel 3a to my Pixel 5a.

That silence ended Thursday morning, when my smartphone greeted me with a notification of a probable exposure. “You have likely been exposed to someone who has tested positive for COVID-19,” the app told me. “COVIDWISE estimates that you were last exposed 5 days ago.”

The app further informed me that “Most people who are fully vaccinated and free of COVID-like symptoms do not need to quarantine or be tested after an exposure.” Fortunately, I had already self-tested negative on an antigen at-home kit Wednesday morning to verify my health before heading to the Hack the Capitol security conference.

Because this app and others built on the Apple/Google code don’t store location data, I can only wonder when this possible exposure happened. And since five days ago was Saturday, when I flew home from Latvia via Munich and then Boston, I’m looking at thousands of miles of possibility. A second notification from COVIDWISE referencing North Carolina’s SlowCOVIDNC app suggests that my possible exposure source lives there, but the privacy-preserving design of this system ensures I’ll never know for sure.

A five-day turnaround, however, now seems quick after seeing three people reply to my tweet about this notification to report that they didn’t get their own heads-up from one of these exposure-notification apps until 10 days after the possible exposure–a uselessly long lag. My conclusion from those data points: Get vaccinated and boosted, because that will do more than anything else you could possibly undertake to ensure that receiving one of these exposure alerts remains a drama-free experience.