With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fnSysSerial
fn Sys Serial
1.3.6.1.4.1.12356.1.2
Device serial number
Back to FORTINET-MIB-280 MIB page.
IPHost Network monitor allows you to monitor fnSysSerial on Fortinet device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Fortinet access points right now.