Which technology allows devices to communicate when they are only a few inches apart?

The correct choice is Near Field Communication (NFC) because it is specifically designed for short-range communication between devices, typically requiring them to be within a few inches of each other. NFC operates at a frequency of 13.56 MHz and is widely used for applications such as mobile payment systems, ticketing, and connecting devices quickly and securely without complicated setup processes.

NFC's unique characteristic of requiring close proximity enhances security since it minimizes the risk of interception or unauthorized access during transmission. This makes it particularly useful for transactions involving sensitive information.

Although Bluetooth also facilitates wireless communication between devices, it operates over a much larger distance, typically up to about 30 feet, making it unsuitable for scenarios that demand close-range interaction. Infrared (IR) technology is indeed capable of short-range communication but requires a direct line of sight between the communicating devices. Geosynchronous satellites deal with long-distance communication to and from the earth, involving much greater ranges, and therefore do not pertain to short-range interactions like NFC.