Would it be possible for a hacker to notice a tracking beacon on the outside of his car?
How long would it take for a hacker with 5 in all programs and 4 in both Hacking and Computer Groups
What modifiers would it give for a radio controlled missle?

Even treating the beacon as a hidden node it seems odd that a hacker should be able to quickly notice it with all the wireless traffic bouncing about.
But I see a tracking beacon as sending an encoded pulse at a few times a second. That should be much more difficult to detect than a node.

I think it is basically the same as detecting a hidden node. If the RT is broadcasting in pulses, it should certainly be harder to detect (as in, damn near impossible unless he's looking for it).

It's less important that the hacker has all the programs, and more important that he has the right ones running; in this case "Scan". (you can only have a handful running at a time without affecting your system's response). In our games, our hacker is a 'novice' role-player, so we just assume her hacker character does things correctly with regards to loading and unloading programs, but when it gets to the details, it's actually a very important choice for a hacker to decide what programs they have running in certain situations.

All that said, I'd only let them find it if they explicitly stated that they scan for it. And then, depending on how "crowded" the wireless traffic was around them, I'd give them a high target number such as 15+, as suggested by the book.

If it only sends out signals intermittently, I would figure out how long they decide to scan for, and then roll a percentage to figure out if they were scanning while it was active.