Add serial number, MAC or IP data points to the product, split the quantity into separate items, and fill them in on site by typing or scanning the label.
Serial numbers are data points. Add a Serial number data point to the product, along with MAC address, IP address or anything else you need, and mark it required if every item must have one.
If a space has several of the same product, open it and use Expand to split the quantity into separate items, so each one gets its own serial number and test results.
On site, fill the data points in on the project's product sheet or on the phone, where scanning the product's label can read serials, MAC and IP addresses into the right fields. Every value is then in the project's CSV or Excel export and on the Assets tab.