So many CFT projects...

1. Hands-off! - Small, mountable, personal alarm system. Attach to a bike, briefcase, computer bag, etc. Arm/Disarm with a key fob. Piercing alarm when someone "moves" your possession. Key fob also has a smaller alarm/buzzer to notify you (up to 10 meters away).
2. mooTracker - Ultra low power GPS tracker for livestock, pets, etc. Can be used with GSM/SMS module, Iridium modem, etc. Uses an accelerometer to detect motion before engaging GPS trackers. Standby current should be <>
3. UV Index Clip - Small (discrete) UV Index sensor (1" square max). Uses a button cell battery, SiLabs C8051F930, and ANT for communication to iPod/iPhone/Pocket-device to alert you when you've had enough rays. Can be clipped to clothing or hat.
4. Crop/Garden moisture monitor. Seed your garden (co-op, winery, etc) with low cost, very low power wireless sensors. They contact a hub (with GSM/SMS capability) to send you status/alerts as text messages. The hub should also support data logging/consolidation for summation or later retrieval.
5. Portable Power Consumption Data Logger. The key word is "portable" here. This data logger/monitor is designed to be used "in the field" with portable devices (sensors, auto accessories, robots, etc). Mainly for battery powered devices. Should be able to measure power consumption between 0-12volt and between 1uA and 3A.
6. WikiReader Portable Terminal - Use the WikiReader as a local/personal display and a controller of UART enabled devices. Maybe use Bluetooth to use it to query/control sensors.

So many CFT projects, so little time. Is there a way to tie them together?

Is there a common theme?

If I only built the things that "I" find useful, which would they be?

I could use #4 in my yard and I have friends that would find it useful.

My wife could use #3....

I could see where #1 would be useful, but it generally sounds pretty boring

(from an implementation point of view).

None of these projects are terribly unique. Maybe my approach is

"low cost / low power". I find it challenging to do a lot with a little.