We describe several diode laser-based instruments that can detect important species in chemical oxygen iodine lasers (COIL). Species detected include: water vapor, atomic iodine, and ground state oxygen. The sensors allow non-intrusive, real-time measurements from which one can determine small signal gain and the singlet delta oxygen yield. The water vapor concentrations can also be continuously monitored. The sensitivities of the sensors are sufficient for all the conditions found in typical COIL devices. The room temperature diode lasers are miniature and fiber coupled. Data for all three species are presented.