I use 433Mhz sensor, with an mqtt<->433Mhz bridge, reaction time is about a second.
And those sensor are pretty inexpensive, under 10€ for Kerui ones for example.
You can find a list of 433Mhz device here: 433toMQTTto433 Gateway Device List
I use 433Mhz sensor, with an mqtt<->433Mhz bridge, reaction time is about a second.
And those sensor are pretty inexpensive, under 10€ for Kerui ones for example.
You can find a list of 433Mhz device here: 433toMQTTto433 Gateway Device List