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.