A sensor assembly includes a sensor configured to detect at least one material or condition, such as a smoke detector, fire detector, or carbon monoxide detector. The sensor assembly also includes a base configured to be mounted on a structure, such as a wall or ceiling, and to receive the sensor. The sensor assembly further includes a wireless module located between the sensor and the base. The wireless module is configured to transmit position information. The wireless module may include one or more electrical contacts used to form at least one electrical connection between the base of the sensor assembly and the sensor. The wireless module may also include a printed circuit board having the contacts, wireless radio circuitry, an antenna, and other components. The printed circuit board could be substantially hidden from view when the sensor is attached to the base and the base is mounted on the structure.