Remind me that I didn't hang up my keys

That is a logic flow, it would require a smartapp to implement.
Helpful reading:
Docs.smartthings.com

Exactly right. This post Connected Smoke Alarms - #26 by pizzinini has a picture of the sensor. I havenā€™t used that particular one myself, but I believe if you pop off the cover, there are screw terminals that should be very apparent. Soldering would make the connection to the posts more secure. Every household should have a soldering iron :smile:.

You could probably even finagle a Lego key holder by using something like http://shop.lego.com/en-US/LEGO-Power-Functions-Extension-Wire-8886. E.g. cut off the one connector, split out two wires and screw to the contact sensor screws. Short out the metal connectors on the other piece (e.g. gluing a strand of wire / foil) and drill a hole for a key ring. Then you hang the key by pushing the key ring Lego piece into the mounted piece, thereby closing the circuit.

This might well be the best solution for someone as technologically inept as myself.I can maybe hide the sensor under the shelf. My one concern is having a magnet in my bag in close proximity to other items like cards with mag strips.

You shouldnā€™t be, I have a wallet with a magnetic money clip and havenā€™t had any issues. The polarity might make a difference but I kinda doubt itā€¦

I got an Ecolink Z-Wave Door/Window Sensor (DWZWAVE2-ECO) yesterday and have played with it a little bit. It seems like a small neodymium magnet is enough to get to register ā€œclosed.ā€

So I just need to attach a magnet to my keyring and then mount the Ecolink sensor under the shelf and then figure out some way of docking the keys that gets the magnet into close proximity to the sensor. So I can see the physical aspects of this KISS solution working.

Now, as a nonprogrammer, the challenge is to find a SmartApp that will make it work.
I havenā€™t been able to find a SmartApp that will do the following:

IF iPhone ā€œpresentā€ (meaning Iā€™m home) <=== I just tested this and the hub thinks Iā€™m present even when Iā€™m not!
AND Ecolink sensor ā€œopenā€ (meaning I didnā€™t put my keys where they belong)
Notify via text message (or SmartThings App)

Any thoughts?