The right not to answer
For its first hundred years the telephone gave the person being called very little choice. A ringing bell was an invitation that was socially hard to refuse, and the caller was unknown until the receiver was lifted. Call screening is the set of methods that gave the recipient a chance to find out who was calling before deciding whether to speak.
Screening by human helpers
Before any device did the job, people did. Switchboard operators and secretaries asked callers for their names and purpose, and then told the person called. In a household, children, servants or neighbors might answer the telephone and report who was calling. This kind of human screening was common in business and in wealthy households, and it was limited to those who could afford staff.
The answering machine as a screening device
The home answering machine introduced a new way to find out who was calling. If the machine played the greeting and recorded the caller’s words through a built-in speaker, the owner could stand nearby and listen. If the voice was a friend, the owner could pick up the receiver and speak, usually interrupting the recording. If not, the owner could let the machine finish.
This became a widespread habit from the 1980s, when machines were common. It was convenient but imperfect. The caller had already been connected to the machine and might have heard a greeting, and some callers hung up on machines. Listening also relied on being close enough to hear.
Caller identification
A more direct method was to show the caller’s number. The idea of transmitting the calling number to the receiver’s telephone was developed by several inventors in the 1960s and 1970s. Patents were filed in various countries, including one by the Japanese inventor Kazuo Hashimoto in the 1970s, though accounts of who first conceived of the idea differ.
The technical requirements were significant. In older exchanges the number of the calling line was known to the exchange only for billing, and there was no standard way to send it to the called line. Computer-controlled exchanges and a signaling system between exchanges made it possible. The number was sent between rings, as a short burst of data, and a display on the telephone or an adapter box decoded and showed it.
Commercial services started in parts of the United States in the late 1980s and spread through the 1990s, along with similar services in other countries. Many telephones with small displays were sold. Some systems could also display the name of the subscriber, matched from a database.
Privacy and limits
Caller identification raised a privacy question. A caller might not want to share a number, for example someone calling from a shelter, a doctor’s office or a private line. Services therefore allowed callers to block display of their number, sometimes per call by dialing a prefix code and sometimes for the whole line. Recipients could in turn choose to refuse calls with withheld numbers. Regulations on this balance vary from country to country.
Caller identification has limits as well. It shows the number associated with a line, which might be shared, such as a company switchboard, or it might be a number the caller has chosen to display. The practice of showing a false number, usually called spoofing, has become common in nuisance calls, so a displayed number is a clue and not proof.
Mobile phones and smartphones
Mobile networks built caller identification into the service from early on, and a mobile phone displays the caller’s name from the contact list when it matches. Smartphones went further by allowing different ringtones for different people, so that a user could tell who was calling without looking. Features such as sending calls from unknown numbers directly to voicemail developed in the 2010s.
In recent years, some phones and services have added automated screening, using artificial intelligence and the same speech tools as voice assistants. Software answers on behalf of the user, asks the caller to say who they are and why they are calling, and shows a transcript on one of today’s touchscreen interfaces while the user decides whether to join the call. These systems depend on speech recognition, whose accuracy varies, and are an extension of the same idea: to give the recipient time and information before answering.
What screening changed
Screening altered the unwritten rules of the telephone. It became acceptable not to answer, and to call back later. At the same time, callers learned to leave messages, and in some cases to text first. The result has been a gradual shift in which a call often has to be requested or scheduled by message, a change that began with a speaker on a tape machine beside the telephone.