Since this is a One building to Many smoke alarm/exit sign relationship, and it seems like you don't need to put points for all smoke alarms and exit signs within each building, a Relate would work better than a Join. You would need a column in each spreadsheet for the building identifier that would match a field in your building feature class (you can also combine all of your spreadsheets into one). Once you've Related your table(s) to your building features, you can configure pop-ups to display summaries (such as count of smoke alarms) of the related data as well as clicking on each related table record to view the details. Once you've selected a building, from the Attribute Table you can also click on "Related Data" from the building's table menu and display all of the smoke alarms/exit signs for that building. The link that David posted to the Joins and Relates describes the process and gives additional links to displaying the related data via attribute tables and pop-ups.
One related recordSummary of related records