Made a plug-in Internet of Things PIR (passive infrared) sensor using the +Spark and a little custom PCB. I am working on something that will let me know if the dog is getting on our bed while we are at work. This way I can remotely monitor the device using cURL from the office.
The PIR sensor goes off when it sees a change in the infrared signature in front of it (i.e. someone walks in front of it). Eventually I am going to add a noise making device to it that should go off when she jumps on the bed and will eventually train her to stay off.
Right now it is using Server-Sent Events (HTML5) so that anything that subscribes to the event gets an indication of the PIR going off, but I can easily update the firmware from anywhere and change how and what I am monitoring in real time without ever unplugging it. I love the +Spark!