An electronic device may include sensors such as a visible-light image sensor for capturing images. The sensors may also include optical sensors that operate at other wavelengths. An infrared light sensor may be used to gather an infrared light spectrum of a target object. The infrared light sensor may have a beam steerer and other adjustable components such as adjustable lenses and adjustable polarizers. During operation, an infrared beam emitted by the infrared light sensor may be steered onto the target object using information from a captured visible-light image and/or other sensor data such as distance sensor data, orientation sensor data, three-dimensional image sensor data, and data from other sensors. Infrared spectra, visible-light camera images, and/or data from other sensors may be used in characterizing target objects so that notifications can be provided to a user and other actions taken.