So, as Phil mentioned, we all got iPhones as a holiday bonus. And they're pretty great. JP and I held off until Macworld, lest we miss out on a new 3G handset (a longshot, I know). When that didn't happen I immediately scurried over to Pentagon City and bought a beautiful internet lozenge.

Since then I've been figuring out all of the amazing things it can do for me. On Thursday I had a stroke of inspiration. I've been looking longingly at Bluetooth presence detection setups for a while. I like the idea of having my hardware respond to my proximity, but I've got some reservations about wasting a Bluetooth dongle (and server, and Bluetooth-on-Linux configuration time) on the effort. The iPhone is the first mobile I've owned that does wifi. This seems like an opportunity to do presence detection on the cheap.

My approach is pretty simple: ping the iPhone. If it's there, I probably am, too. But how to ping it? The iPhone uses DHCP to get an address. At home I've got a router running the SveaSoft firmware. It's simple enough to configure DNSMasq to always dole out the same IP address to my iPhone's MAC.

Then I wrote a bash script to send three pings, check the number of successful replies, and log the result to a text file. I set it up to run on a minute cron and let it go overnight:

PING_COUNT=`ping -c 3 192.168.2.21 | grep "bytes from" | wc -l`
test $PING_COUNT -eq 3 && RESULT="here" || RESULT="not here"
RIGHT_NOW=`date`
echo "$RIGHT_NOW - $RESULT" >> status.txt

Here are the results from the first 24 hours: