MESA, AZ — Mesa firefighter Derek Andresen is going viral - again -for something that has nothing to do with sirens or flashing lights.

After responding to a medical call at a local senior living community, Andresen and his crew made sure the patient was cared for. But before leaving, Andresen noticed a piano sitting in the community gathering space and decided to take a seat.

What happened next stopped the room in its tracks. Residents gathered around as the self-taught pianist-firefighter filled the space with music, turning an ordinary day into an unforgettable one.

The impromptu performance brought smiles, tears, and applause from seniors who never expected a concert from the first responders who had just answered a call.

Someone captured the moment on video, and within days it had been viewed more than a million times online, with comments pouring in from across the country.

Even Andresen's mother joined the conversation, proudly sharing that her son taught himself how to play.

This isn't the first time Andresen has put aside his gear for the keys. During the pandemic, he gathered attention online with another musical performance that delighted the community.

ABC15's Cameron Polom met the Mesa firefighter behind the viral videos and heard from the seniors who were touched by the special performance. Watch the full story in the video player above.