If you connect to Google Play, it will tell you the size of any app for your specific device.
Saying that, Lookout on my Tab is about 8.9MB. Small compared to most games, extra browsers, etc. Yesterday, I d/l NavFree USA and maps for 3 states - that's over 200Mb.
So far, I've only used about half of the available 4.6Gb available for use.
I noticed that Lookout also makes a free app called Plan B that locates your device after it's lost/stolen, though it seems to work better for phones than tablets.