Simulators are tools used in mobile testing to reduce the size of the feedback loop between programming and first exploration, allowing developers to test their code changes frequently. They provide a realistic environment for testing user interactions, such as entering data, clicking buttons, and navigating around, but lack hardware resources like memory and CPU cycles, battery levels, and touch actions. Emulators offer more advanced capabilities, simulating entire devices with hardware resources, but require a stable internet connection to function. Real mobile devices provide the most accurate testing environment, allowing for testing of real-world scenarios, such as device limitations and user interactions, but are only suitable for companies that need to support a limited number of devices and maintain their own test lab. A combination of simulators, emulators, and real devices is often the best approach for mobile app testing.