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Door-to-door is a canvassing technique that is generally used for sales, marketing, advertising, or campaigning, in which the person or persons walk from the door of one house to the door of another, trying to sell or advertise a product or service to the general public or gather information. People who use this sales approach are often known as traveling salesmen, or by the archaic name drummer (someone who "drums up" business), and the technique is also sometimes called direct sales. A variant of this involves cold calling first, when another sales representative attempts to gain agreement that a salesperson should visit.
Products or services sold door-to-door are generally in one of seven industries: cable, telecommunications, solar, energy, security, landscaping and construction. There are also many multi-level marketing products sold door-to-door. The industries accounting for the largest share of direct-sales revenue include construction and telecommunications. The largest subset of these would be the home improvement products/services where items sold could be new or repaired roofs, siding, new replacement windows, and decorative stone. As of 2008 the business model of many companies that participate in this type of direct marketing has changed with the growth of the Information Age. Products sold door-to-door are now more likely to be more subtle in nature: such as sheets of coupons to events or local businesses, season tickets to local professional sports teams (both of these are known in the industry as "Cert [or certificate] Sales", or subscriptions to home television services or broadband internet services. Telecommunications companies like Verizon Communications (FiOS), Comcast (Cable television and internet) and AT&T (U-verse) all contract with various marketing companies for nationwide sales fulfillment at the residential level. While the practice of the salesman carrying a bag of goods on his shoulder to sell to the public declined with advances made in technology and internet selling, there has been a resurgence of door-to-door selling in recent years, especially in the energy and solar industries (SolarCity) (Vivint Solar).
In the United States, some communities attempted to criminalize this form of selling by passing what is known as a Green River Ordinance which bans all door-to-door sales. In 1933, the United States Court of Appeals for the 10th Circuit upheld such a law valid  but in 1976 the Supreme Court extended the First Amendment to commercial speech and in 1980 set forth a four-pronged test regarding the regulation of door-to-door selling:
If a regulation meets these criteria, it is most likely legal.
In 2011, door-to-door sales was named one of the top 10 dead or dying career paths with an 18 percent decline in positions expected by 2018. Instead, between 2012-2013 door-to-door sales positions started growing 34% year-over-year. In 2017 the market is believed to be worth $36 billion, an increase of $7.7 billion since 2009 (or $4 billion if adjusted for inflation). As of 2017, the research shows that 20.5 million people in the United States have signed agreements with direct selling companies making them eligible to purchase discounted products and resell them that at a profit, and to sponsor others individuals who also can sell the products.
New technologies have also changed door-to-door sales' efficacy and appeal for organizations. Expansive databases of American households pull together demographic information, consumer data, and past-canvassing profiles to allow precise targeting of potential buyers. Corporations no longer knock on all the doors in an area, instead they focus on people most likely to buy their products or services, using targeting tools like Polis, for example.
Police detectives many times will go door-to-door at residences that exist nearby a crime scene, to see if the victim or perp may have known (or may have been known by) any of the residents in the general vicinity, or to gather information from potential witnesses.
Some Christian groups, such as Jehovah's Witnesses, and to some extent the Seventh-Day Adventists and The Church of Jesus Christ of Latter-Day Saints, are known for door-to-door evangelizing and proselytizing.