Is Dave across the desk from you working at the moment? Or is he goofing off? You can’t see his screen but I reckon you can make a fair stab at what he is up to, without recourse to any sort of IT monitoring systems at all. How?
How fast is Dave typing?
If Dave is typing fast, he is almost certainly not working. He’s goofing. There are very few things you can do when you work in IT where you type fast – and especially not type fast for more than a few seconds. If Dave is typing fast he is almost certainly emailing a mate or instant-messaging Sandra in the development team. If Dave is typing fast, pausing for a few seconds and then typing fast again, he is *certainly* conversing electronically with a friend. This will be 100% corroborated if he smiles, sniggers, smirks, laughs or just glances around furtively.