How would you use SNMP to determine if a switch stack member went down?

I have some access switches in stacks. Since they're access switches, I don't really want to monitor the individual interfaces because I don't really care when people turn on/off their workstations. But I DO care if a whole switch within the stack dies. Note that the stack IP address continues to stay up and SNMP polling continues just fine. How do people determine if a switch member goes down? I know the "ifNumber" interfaces MIB SNMP object will change to reflect the reduced number of ports... is that what I should be alarming on?

(I'm Using Cisco 3750 & 2960 switch stacks and Intermapper for polling, but I'm also interested in how people would do it for other products too)