Optical systems are quiet common. Using either the UV spectrum to look for the distict exhaust plume of a missile, or IR systems to see the heat of the missile, again, most noticably the exhaust gases. Maybe even a combo. Those systems are on a number of airplanes. (You might have noticed that sometimes the MAWS in the J-11B was debated in the "China Flanker thread")
The active radar MAW is used in the Eurofighter for example. Though I haven't found any new reports on it lately.
Those systems all have their (dis)advantages, being themselves active / passive and so on. The EF MAW was to replaced by an IR system (PIMAWS) later in tranche 3 maybe. But I'm not sure if it will ever materialize.
On a side note. There are directed infra red countermeassures. Thats an IR laser that will dazzle an IR missile seeker by sending laser pulses at it. The USAF will mount those on C-17, CV-22, CH-53 for example. There was also talk of a microwave version, that'll barbecue radar missile seekers.