Add a remote ringer
The most difficult part of adding a new ringer is tracking down the cables. Although it's easy to connect a new “doorbell cable” (common is 18- or 20-gauge CL2 type or the equivalent) at the existing doorbell chime, it may be difficult to run concealed wires to a basement shop or other remote location. It may be easier to make the connection at the low-voltage transformer that powers the doorbell, especially if it's near the shop. Often the transformer is mounted on the electrical service panel.
If you're connecting it at the chime, note the three screw terminals labeled “front,” “back” and “transformer.” Connect a wire to each and then simply make sure the three wires connect to the same terminals on the new chime. There's no uniform color-coding for doorbell wires.
Add a second chime cable at the transformer, exactly like the cable to the existing chime. Your existing transformer may not be powerful enough to handle both chimes. So if you get a weak sound, replace the transformer with a 15-20VA (volt amp) unit.