A drum trigger is a microphone. Nothing more. It picks up the sound of the drum and sends the audio to the source. The source usually is an audio to midi converter either in the box or outside of the box, but that doesn’t have to always be the case. The audio from a kick trigger, for example, can be sent via side chain to a compressor that is set up to duck the bass guitar around the kick. The audio from a snare trigger can be used to open a gate that lets the snare drum mic through, which is a widely used trick for controlling snare bleed because the gate is reacting to only the transients of the snare trigger. But no matter how you use them, a trigger is effectively nothing more than a microphone. What you do with them is up to you.
This is how applications like Slate Digital’s Trigger work. There’s an internal threshold, and once the transient of the drum goes above that threshold it tells the software to trigger the samples you’ve loaded. Depending on the intensity of the transient, Trigger can decipher what the intended velocity would’ve been of the drum hit and play a sample that matches what the drum would’ve sounded like at that velocity.
A Drum Module is little more than an audio-to-midi converter that plays samples triggered by the incoming transients. If I were to connect a microphone into the drum module, and clap my hands, that clap would trigger a drum sound at the module. Just like with Trigger, an internal threshold was crossed which told the drum module to play the drum you’ve chosen. You don’t need a drum trigger to use a drum module, but a drum trigger produces an audible transient with no bleed from the rest of the kit. That makes using a drum trigger easier and more accurate than using a microphone for the same purpose.
That’s not to say that a microphone can’t be used as a drum trigger. Remember that Trigger uses any audio source, and not just a transient from a drum trigger. To demonstrate this, here’s a video of a guy using cardboard boxes and a drum throne as drum triggers.
The important thing to remember is that drum triggers merely transmit an audio signal, which is exactly what your microphones are already doing. They may have different typical applications, but they are nothing more than microphones that are very well isolated from the sounds surrounding the source they’re touching. Knowing this, try to find some creative new ways to use drum triggers or incorporate them into your productions!