Sending and receiving information with electromagnetic radiation is fundamental to imaging and communications. Humankind’s ability to utilise this radiation is dependent on how efficiently we can detect it, and improving detectors will advance these technologies. Visible light and X-rays make up two regions of the electromagnetic spectra, both key bands for imaging in different modalities. The visible spectrum represents the energies we can detect with our eyes, while X-rays are highly penetrative and allow the inside of opaque objects to be imaged. While their applications are highly complementary, their detector technologies also share commonalities, allowing the development of both simultaneously. In this thesis, the unique properties of metal halide perovskites are utilised to advance both visible light and Xray detectors. However, other properties of perovskites, such as ion migration, can provide challenges when characterising performance, and so techniques to accurately measure their detecting ability are also developed. Metal halide perovskites are exploited to design two new detector device structures, increasing the functionality of photodetectors and overcoming the existing limitations of direct X-ray detectors. A unique photodetector, utilising the band gap tunability of perovskites, is developed to produce a multiband response that can controllably detect different regions of the visible spectrum. The resulting device is employed in a method to send communications with added encryption. Additionally, a concept for a novel X-ray detecting device is developed, using the ability of perovskites to retain impressive properties after low-temperature solution deposition. The device structure decouples the dimensions of photon absorption and charge carrier collection to retain performance across the X-ray spectrum, overcoming the limitations currently preventing the commercial success of direct X-ray detectors. The potential of perovskites as scintillators for indirect X-ray detection is investigated. The published performances are contextualised with a detailed analysis of the operating mechanism. This mechanistic insight highlights the advantages this material could bring, and we propose the applications that would benefit most from perovskite scintillators, as well as the origins of the remaining limitations. The concurrent understanding of perovskites in other optoelectronic devices is utilised to suggest pathways to overcome the remaining challenges and bring the material closer to commercialisation. These suggestions are applied, and impressive scintillation performance is demonstrated from an emerging Cs2ZrBr6 nanocrystal scintillator system. This work also highlights the specific considerations required when characterising perovskitebased detectors. The large defect density in these materials is shown to be a double-edged sword; making measurements under low light intensities prone to errors, but also acting as another lever to control detection performance. The challenges of characterising direct X-ray detectors are also discussed, alongside the development of experimental procedures to robustly measure halide perovskite devices. Overall, this thesis utilises the unique properties of perovskites to develop detectors with new functionality, whilst ensuring the same properties do not reduce the accuracy when characterising their performance. The work brings perovskite detectors one step closer to a commercial reality.