True, there are a bewildering number of choices out there, but I think the XBee is one that gives you the most bang for the buck. Granted, they are not exactly banned, and you can make your SEWS (Spousal Early-Warning System) much more cheaply with simpler hardware, but I recommend the XBee because I guarantee that once the wireless bug bites you, you'll want to do more and more other things, especially after she catches on to what you are doing and makes you take it down!
Just a few things I like about that platform:
1. Lots of on-board connection choices- TTL serial port, discrete digital I/O, and analog inputs (last time I looked, XBee series 2 does not support analog outputs, but it is possible with the on-board hardware with future firmware)
2. Several different operational modes:
(note- modes are determined by the firmware you load, and are mutually exclusive. Pick the one you need- you can always change it later)
a. Direct transmission of digital I/O states between transceivers, without the need for a host microprocessor on each end.
b. Serial Port pass-through, basically a two-way dumb wireless serial "cable."
c. API Mode, which allows you to package your data into telegrams with robust transmission and data integrity verification. API Mode also allows you to do a whole host of other things related to the configuration and operation of the device itself. (requires a smart host to build and decode the data packets. Arduinos are great for that)
3. Function is determined by firmware, which makes the XBee fairly future-resistant.
4. Series-2 XBees can be used to build mesh networks (tres cool!) which is a great way to extend the reach of low-powered modules.
5. Can be exposed to the Internet, via a dedicated Gateway module (separate hardware, also mfg by Digi, the makers of XBee)
If you decide to get started, here are some tips:
1. Brace yourself (and DW). Playing with XBees is like eating potato chips. It's very difficult to stop.
2. Buy the regular Series-2 modules. No need to get the Pro units (extra power and range). You'd be amazed at what the "regular" ones can do.
2. You will need at least two, but buy three. Trust me. (Note Series-1 are point-to-point only, and do not support mesh networking)
4. Because of the wonky 2mm pin spacing, you will need a breadboard adapter for use with standard 0.1" breadboard grid. There are many interface boards out there, but the best one, by far, for beginners is this one:https://www.adafruit.com/products/126
it's very well-designed, with a lot of useful features, and worth every penny!
5. For configuring your units, you will need a TTL to serial adapter, such as:https://www.adafruit.com/products/70
They both are functionally equivalent, and will plug directly
into tha Adafruit adapter board, a very useful feature!
The Firmware configuration and setup is accomplished with a software tool (X-CTU) that you can download and use for free from Digi.
and finally, perhaps most importantly...https://www.adafruit.com/products/963
The definitive XBee Reference Manual. I have had my worn, dog-eared copy for over a year, and I still use it regularly.
These things are a blast, and if you have the budget, loads of fun!