Let's Control It

I have a system that when in active mode it closes a circuit.
Can it be monitored by ESP Easy ?

Thinking like setting a gpio to output 3 volt and another gpio as input.
And when Input gpio got 3volt it sends a MQTT message

Can it be done ?

i think this should be possible ...
i would try sending a digital signature (GPIOx high,low,high,low,high) and try to receive this pattern at another GPIO.
How long is your circuit? is there another powersource?

I plan to set the ESP with in 10cm from the system with the circuit.