Which wireless communication technology has a very limited transmission range of less than two inches, is used with credit cards and passports, and constantly emits a signal?

NFC, or Near Field Communication, is a wireless communication technology that indeed has a very limited transmission range, typically less than two inches. This short range is intentional, as it enhances security by ensuring that devices must be in close proximity to exchange data. NFC is widely used in applications such as mobile payments with credit cards, contactless payment systems, and secure access for passports, allowing easy and secure communication between devices.

One of the defining features of NFC is its ability to constantly emit a signal, which allows it to establish communication with other NFC-capable devices simply by bringing them close together. This makes it convenient for users who want a quick and intuitive way to interact with payment terminals or other NFC-enabled devices without requiring manual pairing or complex setup processes.

In contrast, Bluetooth has a much longer range and is typically used for connecting devices over several meters. Wi-Fi operates over a wider area and is generally used for high-speed internet connectivity rather than close, secure transactions. Infrared technology also has a limited range but relies on line-of-sight communication and does not actively emit a signal, differing significantly from the operation of NFC.