This should work, but only if you have more than 100 items, because it will get confused with the time (Eg It could take 12:30 and think you have 30 items). Because of this, I've made it parse for numbers higher than 3 digits.
I didn't test it with more than 999, but it should work.
This should be an action, not an action wpt.
local alarmValue = 100
local serverLog = getnewmessages("Server Log")
local serverLogLine = serverLog.count - 1
for i = 0, serverLogLine do
if serverLog[serverLogLine - i].text:find("Your depot contains") then
for j in string.gmatch(serverLog[serverLogLine - i].text, "%d%d%d+") do
if tonumber(j) >= alarmValue then