can you have 2 Simplisafe systems and use....

I think that if you register the second system to the same account, then when you go into the app, it asks you which one you want to access.

Yes, absolutely you can do that under one login if, as sevensiamesecats mentioned, they are both on the same account. Just give each system a unique name then you can select which system you want to arm/disarm etc. Push notifications from either system come through regardless which system is currently selected.

I have it this way. Two systems; East and West. Just "click" the House icon in the top right of the app dashboard to choose the system.

My original system was automatically completely deleted as soon as I added the new base station, including a smoke detector I believe is compatible with the new system. Said smoke detector is nearly 20 ft high, so I have not been able to add it to my new system, since I don't know the serial number. On the bright side, all of the components for the new system were automatically added.

SimpliSafe probably could find the serial number. On the other hand, it may be faster to figure out how to reach the unit at 20ft.

Plus, it has to be cleaned once a month or so, otherwise be prepared for numerous false alarms when you finally do add it to your system.