Combination Smoke Alarms

Does anyone know how combination smoke alarms behave? Will either sensor sound the alarm, do both need to be activated, or does it vary from one unit to the next? An answer and examples would be appreciated. Thanks

It depends on the type of fire

What I’m trying to ask is if either sensor trips, will the alarm sound, or do they both have to sense smoke.

If one sensor triggers. The unit will go into alarm