Why Eric Schmidt has a 15-year-old door stored in his fancy Google office ‎

Alphabet executive chairman Eric Schmidt keeps an extremely old door in his office. It was his desk when he joined Google, the billionaire told the Startup Grind Europe event in London on Wednesday.

When he was hired 2001 as chief executive to run the search company, he was in a small office and his desk was a door resting on a stand.

Eric Schmidt, chairman of Alphabet Inc
Marlene Awaad | Bloomberg | Getty Images
Eric Schmidt, chairman of Alphabet Inc

He said he keeps it as a reminder of his humble beginnings and what it took to make Google one of the most valuable companies in the world.

"I can always tell when we're dealing with a proper founder when we start with how are they spending their money. And so whenever I go into [a] start-up that has beautiful offices, really nice chairs, I cringe. Because that means I haven't quite figured out that it isn't their money," Schmidt said.

"When I joined Google, I was is [in] an office and I had a little corner of a desk with four other engineers. Eventually I was given an 8-by-12 office where my desk was a door, ... a tabletop, literally a door, which I retained to try to remind myself of what it takes to be successful, so my office today has that door in it."

"I can always tell when we're dealing with a proper founder when we start with how are they spending their money." -Eric Schmidt, Alphabet executive chairman

Schmidt was talking about what qualities he looks for in successful entrepreneurs when Alphabet considers where to invest. The U.S. technology giant has an investment arm called Google Ventures, which invests in start-ups. One of the key traits is that founders should be frugal to the point of not taking salaries.

"The great founders are frugal, they understand that the money needs to be used precisely for certain areas, many of the most successful founders began with no salary at all," Schmidt said.

In 2004, Schmidt and Google co-founders Larry Page and Sergey Brin, opted for $1 annual salaries, although they had stock options worth considerably more.