Passing a joint is becoming increasingly passe. Pax Labs Inc., a San Francisco-based startup that makes marijuana vaporizers, is now valued at $5 billion, said two people familiar with the company who asked not to be identified discussing the terms of a private deal. The company raised $20 million in its latest funding round, according to Pax Chief Executive Officer Bharat Vasan. Pax, part of a rising tide of marijuana device companies, makes internet-connected vaporizers that allow users to control how high they get when consuming the drug. The company's sleek devices look like highlighter pens or USB sticks, and are operated through an app.