The detections of $\gamma$-ray sources coincident with a Gravitational Wave event and an ultra-energetic neutrino officially started the era of multi-messenger astrophysics. These two ground-breaking announcements demonstrated that monitoring the sky in $\gamma$\ rays will be fundamental to identify the electromagnetic counterpart of transient events and promptly trigger follow-up observations, aiming at the full characterization of the signal.
In recent times, our ability to study high-energy $\gamma$\ rays greatly improved, particularly through the use Imaging Atmospheric Cherenkov Telescopes (IACTs), which will reach unprecedented performance with the Cherenkov Telescope Array (CTA). These instruments, however, have limited duty cycle and field of view, lowering their efficiency in the observation of transients, if not properly alerted. Extensive Air Shower (EAS) arrays, on the contrary, can survey large areas of the sky and provide prompt information on high-energy transients, working in combination with other observatories. Here, we present the Southern Wide field of view Gamma-ray Observatory (SWGO), a new EAS facility designed to monitor the Southern sky, from $\delta \simeq +27^\mathrm{o}$ down to approximately $-73^\mathrm{o}$. We describe the issues that such an observatory needs to address to operate down to the sub-TeV energy range, and the advantages that would result from their solution.