Modern shark researchers have access to a variety of high-tech tools. Acoustic tags with noises specific to each individual shark signal a receiver (or network of receivers) every time the shark passes nearby. Some tags have three-dimensional accelerometers, allowing researchers to study the small scale movement patterns and behaviors of sharks. Others, which are placed in the stomach, measure pH before, during, and after digestion. The most advanced technology on the market, however, is undoubtedly the satellite tag.