The ESP8266 can be set to deep sleep. You need to connect GPIO-16 with the RST pin to make this work.
If you enable Sleep Mode, the ESP will send all the sensor-readings at once and then go to deep sleep. It will sleep for the amount of seconds thats set in the Sleep Delay setting.
This saves lots of power, allowing you to use the ESP8266 on batteries.
Note that its recommended to set the Message Delay to 0 in the advanced settings page.
Using Deep Sleep Mode for battery-powered devices see here.
Getting out of deep sleep
When this state is active, you can't connect to the web interface. In fact, the ESP is turned off and only a dedicated timer circuit is still powered to wake up the main ESP core.
There are three ways to get out of sleep mode:
Power off the ESP and reconnect power. You will have 30 seconds to connect to the Web interface and disable the Sleep Mode function. (You will get feedback in the serial interface)
Temporary disable Deep Sleep via jumper setting
If 30 seconds is too short for you, you can use this method.
Disconnect D0 from RST and connect it to GND. Restart your ESP if neccesary.
Now deep sleep will be disabled and your ESP will function normally, until you connect D0 to RST again.
This requires ESPEasy v2.0.0-dev6 or newer.
If all else fails, just do a factory reset. You will lose all your settings!
Connect the RX and TX pin together while you restart your ESP.