Often a very useful and efficient intrusion detection device, honeypots have been around for a long time, but now are getting more sophisticated and complex. Honeypots are devices (often just an old pc), connected to the internet or a network, which contain features designed to lure hackers. For example, they might contain fake bank login information of credit card information resident in places where hackers might look.
Software is available for honeypots, which not only sets up the lures, but also detects and records the activities of intruders. Any intruders are deemed to be suspicous.
Most systems connected to the internet should have honeypots. They are simple to install and cost effective to run, having virtually no maintenance cost.
For a series of excellent articles on honeypots as well as some reviews of current honeypot software, check out this link.