Arduino Sim800L

The smallest and cheapest way to add cellular SMS and GPRS to a project, but also the least forgiving. The SIM800L is a bare module with no onboard regulator: it must be fed 3.7-4.2V, and 5V will destroy it. It also draws current bursts up to 2A when transmitting, which is why the single most common failure is a module that resets every time it tries to connect. Power it from a LiPo cell or a dedicated buck converter with a large capacitor across the supply, never from an Arduino's 5V pin. Get the power right and it is excellent value. Very small footprint for compact and battery projects; SMS, voice and GPRS over 2G; AT command control over serial; Onboard status LED shows network registration