ماژول SIM800L میکرو سیمکارت

Module type: SIM800L 
Working voltage: 3.7~4.2V 

The size of the module: 2.5cmx2.3cm

TTL serial port, can be directly linked with single chip microcomputer. Don't need
MAX232
Automatic startup power module, automatic network

Onboard signal lights all the way.

It flashes slowly when there is a signal, it flashes quickly when no signal.