In contrast to the multi-color detectors, the measuring signal is available in a series through the very same optical and electrical channel.
Dual channel pyroelectric infrared detectors (Channel1 = sample gas, and Channel2 = optical reference) are used in sensor modules of many manufactures that build NDIR Gas analyzers. The 4-pin TO39 package in which the Pyroelectric chips are integrated, along with JFETs and high Ohm resistors is a standard.