In Iraq, owning this special item can grease the skids in business, get a politician to stand at attention and even inspire affection in a sweetheart.
This key that opens so many doors is a cellphone SIM card.
But not just any SIM card. It must be "distinguished," associated with a phone number considered prestigious because it has a distinctive or beautiful series of digits. Say, for instance, a string of sevens or zeros, or a repeating pattern of numerals.
The marketplace for these modest pieces of plastic inside phones, which connect them to a network, can rival that of gold and precious stones - with trades in the thousands and tens of thousands of dollars.
And while this market emerged about a decade ago, a newfound optimism in Iraq's future after the recent defeat of ISIS in Iraq has increased demand for the special SIMs among aspiring business executives, political neophytes and young people looking to treat themselves.
They've become so popular that Iraq's largest telecom companies are formalizing the trade, introducing offers for tiered SIM cards from "Silver" to "Diamond Plus." A regular SIM card runs about $3, while a Silver card carrying a number with some combination of consecutive pairs, such as 4455, costs about $30. A Diamond Plus card - which features a number whose last five digits are the same - will set a seeker back $1,300 to $1,500.
But it's on the street and in internet chat rooms - where the trend was born - that the big-money cards, also known as "presidential numbers," are found.
The value of the cards is derived not from numerology or lucky dates but from what the number conveys to others about the phone's owner.
"These numbers are a language," said Haider Mohamed, a 45-year-old cellphone dealer who specializes in distinguished phone numbers. His shop, "World of Distinction," located in a shopping strip in central Baghdad, advertises the special permutations available for sale on long sheets of paper displayed in the window.
"A man makes calculations for what will make him successful in life or in business," Mohamed said. "Among them is what his phone number says about him."
And what does a phone number with the right combination of consecutive zeros and ones say?
"It says he has taste. It also says he's loaded," Mohamed said, breaking out into laughter. "It gives him optimism. It gives him prestige."
Mohamed said he once traded a particularly beautiful number to a businessman for a $60,000 Lexus, a claim confirmed by Mohamed's top rival in the prestigious numbers business.
Owners of the numbers and the merchants who sell them generally agree the trend began sometime in 2007 - a result of Saddam Hussein's ouster in 2003 during the Iraq War. Iraq, long cut off from the world by punishing sanctions and pariah status, began to open up; new technology and foreign products started to pour in. Cellphones were among the most coveted items, especially in a country where few people use landlines.
Iraqis became brand-conscious in everything from cars to clothes. Luxury items that once were within the reach only of the narrow ruling elite flooded the market. If you had money, you could express your individuality through what you wore, what you drove and what you carried.
The toppling of Hussein also shattered the tight political and business class that had surrounded him, creating opportunities for savvy entrepreneurs and ambitious would-be power-brokers. To project status and sophistication, they needed the right tools. An impressive phone number became indispensable.