How does the Missile lock-on alarm in an aircraft work?

both air/air , surface/air systems work in same way. radars search, acquire/track, , launch. don't want radar design, these different modes operate on different frequencies (sometimes different radars). receiver(s) in target aircraft detect, classify , display information crew. library of processors enable system determine signal is, , relative threat.
threat system in lock-on/launch more serious 1 in search mode.
depending on sophistication of electronic counter measures, jammers automatically start disrupting radar energy threat. can start automatically dispensing chaff-which anodized aluminum pieces cut 1/2 wavelength of common threat radars. these show huge return, masking aircraft.
finally, 1 starts visual scan pick launch signature. combination of 3 measures used defeat missile (air/air or sam)
ir missiles can detected during launch, circuitry both find distinct ir flare of missile, , ignore other ir energy complex. it's close, not quite mature technology radar. (laser countermeasures not unlike ir in regard.)
if 1 detects ir launch 1 dispenses flares, burn @ higher intensity engine exhaust. there's other type decoys available. since it's had pick out missile which, typically 1 drops both flares , chaff simultaneously.

how aircraft know whern being locked on. (please give answer both heat-seeking , radar missiles)

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