Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

You can plug the device into the wall outlet and check the functionality of the wiring.

They sent me an electronic invoice from locksmith.

I prefer tenants pay using electronic ACH transfers through apartments.com and in those cases payment is considered made when they initiate the transfer even though I don't receive the money for days afterwards.

If the software is not simplifying your life or making you more accurate, you shouldn't use it.Software does have extremely helpful features like online payments, marketing syndication (click a button and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

Many landlords now use online platforms that integrate electronic signature capabilities to handle this legally and efficiently.

The electronics package is very sensitive to fluctuations in electrical supply. 

Ours were not electronic, they would fill them out at the property if they were interested, or drop them by later. 

The tenants are so easy to manage and all pay on autopay electronically.

You'll need to figure out how to wire it (it's not that tricky, a lot of devices have a 12v power supply) or pick a different model that can plug into a wall but has similar specs.