Working out in the 'Mirror,' an interactive home gym

What started as a prototype not much bigger than a laptop is now a nearly invisible interactive home gym.

Brynn Putnam created Mirror after she had an aha moment and realized she could create a mirror that could function as a gym.

When it is off, Mirror looks like a beautiful full-length mirror. When it turns on, you can see yourself, your instructor, your classmates, and your personalized metrics and form tips.

Brynn, a former dancer with the New York City Ballet and the founder of Refine Method fitness studios, had that aha moment when her busy life kept her from going to her own studios and she realized she wasn't the only person looking for an easier way to get in a workout.

Brynn says working out at home always meant sacrificing quality for convenience. She thought about a treadmill or a bike but didn't want big clunky equipment in her living room.

She tried streaming apps and websites but they weren't interactive or immersive.

Mirror costs $1,495 plus $39 a month for access to classes, which include cardio, strength, Pilates, yoga, boxing, barre, and stretch.

Brynn says they film 50 new live classes each week. They record all of the classes in a production studio in the Mirror offices in Manhattan. Those classes are also available on-demand in the Mirror library so you can access them anytime.

A corresponding smartphone app and heart-rate monitor customize Mirror for you, so the mirror actually responds in real time to your preferences and your biometric feedback. That means you're actually delivered exercises that are a fit for you at that exact moment, Brynn says, so you're never going to have an exercise that's too hard, too easy, or not right for your body.

Brynn has raised more than $38 million in funding from some of the top venture capitalists in the country, including Spark Capital, Lerer Hippeau, and First Round Capital, who don't see Mirror as just another fitness fad.

Brynn says Mirror is a workout-agnostic platform. As consumer tastes change, Mirror can change as well. If you're into barre today but boxing tomorrow, the platform can give you the type of content you need, personalized for you.