Ambient backscatter is a novel wireless communication technique that enables devices to communicate using ambient RF signals as the only power source. This approach leverages existing TV and cellular transmissions to eliminate the need for batteries or wires, enabling ubiquitous communication at unprecedented scales and in previously inaccessible locations. The system uses backscatter communication, where devices reflect ambient RF signals to convey information. This method is significantly more power-efficient than traditional radio communication and does not require a dedicated power infrastructure. The design of ambient backscatter involves a hardware prototype that harvests energy from TV signals, uses UHF TV signals in a 50 MHz wideband centered at 539 MHz, and includes components for communication, touch sensors, and LEDs. The prototype achieves information rates of 1 kbps over distances of 2.5 feet outdoors and 1.5 feet indoors. It also demonstrates the feasibility of two applications: a bus pass that can transfer money and a grocery store item tag that detects misplaced items. The system's performance is evaluated in both indoor and outdoor scenarios, showing that it can operate battery-free at distances up to 6.5 miles from a TV tower. The design includes a network stack that enables multiple ambient backscatter devices to co-exist, with a focus on energy detection, carrier sense, and interference management. The system uses analog components to decode backscattered information, leveraging the difference in communication rates between ambient RF signals and backscattered signals. The prototype's power consumption is optimized, with the microcontroller and sensors contributing to the overall power budget. The system's effectiveness is demonstrated through experiments showing that the power ratio between non-reflecting and reflecting states is around 1.4, which is favorable for backscatter communication. The system is also tested for interference with TV signals, showing that it does not create noticeable glitches on standard TV receivers when the device is more than 7.2 inches away from the TV antenna. The design contributes to the development of energy-efficient, battery-free communication systems that can enable widespread, low-power communication in the physical world.Ambient backscatter is a novel wireless communication technique that enables devices to communicate using ambient RF signals as the only power source. This approach leverages existing TV and cellular transmissions to eliminate the need for batteries or wires, enabling ubiquitous communication at unprecedented scales and in previously inaccessible locations. The system uses backscatter communication, where devices reflect ambient RF signals to convey information. This method is significantly more power-efficient than traditional radio communication and does not require a dedicated power infrastructure. The design of ambient backscatter involves a hardware prototype that harvests energy from TV signals, uses UHF TV signals in a 50 MHz wideband centered at 539 MHz, and includes components for communication, touch sensors, and LEDs. The prototype achieves information rates of 1 kbps over distances of 2.5 feet outdoors and 1.5 feet indoors. It also demonstrates the feasibility of two applications: a bus pass that can transfer money and a grocery store item tag that detects misplaced items. The system's performance is evaluated in both indoor and outdoor scenarios, showing that it can operate battery-free at distances up to 6.5 miles from a TV tower. The design includes a network stack that enables multiple ambient backscatter devices to co-exist, with a focus on energy detection, carrier sense, and interference management. The system uses analog components to decode backscattered information, leveraging the difference in communication rates between ambient RF signals and backscattered signals. The prototype's power consumption is optimized, with the microcontroller and sensors contributing to the overall power budget. The system's effectiveness is demonstrated through experiments showing that the power ratio between non-reflecting and reflecting states is around 1.4, which is favorable for backscatter communication. The system is also tested for interference with TV signals, showing that it does not create noticeable glitches on standard TV receivers when the device is more than 7.2 inches away from the TV antenna. The design contributes to the development of energy-efficient, battery-free communication systems that can enable widespread, low-power communication in the physical world.