Two versions of the Trinket are available, a 3V and 5V. Use the 3V for sensors and devices that need 3V logic, 5V for sensors, and devices that need 5V logic. The Trinkets can be powered with a LiPo battery and the 3V version should only run at 8MHz. The 5V version can run at 8MHz or at 16MHz by setting the software-set clock frequency. Even though the Trinket can be programmed using the Arduino IDE, it's not fully 100% Arduino-compatible.