The device that enables the wireless detection of infrared signals is a(n) _____.

A phototransistor is a semiconductor device that responds to light, including infrared signals. It operates by generating a measurable electrical current when it absorbs photons from light sources. This ability to detect infrared signals makes phototransistors particularly valuable in various wireless communication applications, such as remote controls, data transmission, and sensing devices.

While other options like photovoltaic cells are primarily designed to convert light into electrical energy, they do not serve effectively as detectors in the same way phototransistors do. Infrared LEDs emit infrared light but do not detect it, and thermistors are temperature sensors that do not operate based on light detection. Therefore, the phototransistor stands out as the device that specifically enables wireless detection of infrared signals.