I'm using a ZigBee button to call an automation which notifies via Pushover and Alexa. Works fine.
I'd like to reduce latency and use a physical button. I can use a Pi, ESP32 or similar to respond to a closure and tell HA.
What's the lowest latency input to HA? My MQTT server is separate so I'm thinking an HTTP post direct into HA might be best.
Is there anything faster? HTTP is fast enough in my testing, it's an experiment as much as anything else.
I don't think that MQTT could add any perceptible latency. Maybe is the button itself that adds it. Isn't the button able to recognize multiple pushes? If yes, there lies the delay: the button waits for a second push and if it doesn't arrives, it sends out the command to the coordinator. What kind of ZigBee button are you using?
That's a good point; the button does support double push, I might be able to disable that. It's some old unit I picked up for next to nothing, I have some Aqura buttons about to try.