Hello,
Lansweeper has 2 built-in reports that can assist you in finding new scanned computers or devices found in the last 24hrs. These reports are called "Device: New devices found in the last 24 hours" and "Computer: New computers found in the last 24 hours".
Next to this you could also use Asset Radar to find devices that appear on your network:
https://www.lansweeper.com/knowledgebase/asset-radar/
With the current setup report alerts are being send out using a schedule, they will not be sent out the moment a new device pops up. You could schedule them to run 15 minutes for example.