From Chris Gummer:
HIIT Timer is an application designed for your High Intensity Interval Training. HIIT Timer gives you a fully configurable interval timer on your iPhone and iPod touch.The application counts each set for you and uses a classic digital display for time. HIIT Timer is designed to alert you of the current interval at all times. Your iPhone or iPod touch can be rotated to provide an extra large time display. Sounds can be configured to alert you of the start of each interval.HIIT Timer has the following features: Configurable time intervals for both high and low stages Coloured backgrounds signifying the particular interval Set counter Sounds are configurable to indicate the start of each interval Vibration (iPhone only) to indicate the start of each interval Sounds effects and/or vibration (iPhone only) may be turned off Extra large landscape display Classic digital time display Auto-lock can be disabled to prevent screen locking during intervals Tap anywhere on the screen to start/pause Saves timer position on exit Save custom timers for your workouts Runs in the background on devices that support multitaskingNote: If your intervals are being interrupted by your device's Auto-Lock feature, then please switch "Auto-Lock" to off in your HIIT Timer's Options screen.