I assume you are referring to the --watch option of mii_tool which is no longer available.
A couple possible ways to proceed:
1) All link state changes are logged to syslog on the gateway by default. If the gateway syslog server is configured to forward all its entries (or just the ones you want) to an external syslog server such as Splunk, that system could watch for these link state change events and fire the alert you want.
2) You can also create a custom SNMP trap to do this from the Gaia web interface, you'll just need to figure out the OID for a link state change in the proper MIB.
3) Also check out the threshold_config command mentioned in sk90860 which may be able to do what you want.
4) Finally you could configure forwarding of all gateway syslog logs into the normal Check Point logging mechanism as specified in sk102995, then configure an Automatic Reaction in SmartEvent if you have that product available in your environment.
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