Density, a startup developing occupancy-tracking radar sensors, has raised $25 million in venture capital. : Density, a startup developing a range of people-counting, AI-powered sensors, today announced it has raised $25 million. Density says the capital will be used to accelerate growth and scale initiatives as it releases an addition to its software suite called Portfolio. In many respects, Density’s products were tailored for a health crisis. Cities around the world have imposed limits on businesses — particularly restaurants — regarding the number of customers they allow in.