Hey guys, I'm new to Arduino and to the community (after a few years break from AVR - back then playing with assembler and C) and have an idea for a simple signalling application. It would involve wireless communication inside an apartment building (over some 12 floors - from the front door - the distance is <40 meters but the concrete walls are the main worry). The communication would be very basic and in the initial stage, it wouldn't even to send any data - just a beacon signal every few minutes once activated. Later, perhaps, it could send a few bits of data, such as temperature reading and battery voltage.
Since I'm more into software than into hardware, I'm wondering if such a wireless connection is feasible at all at low cost and any guidance would be appreciated. I guess the main questions are: what kind of RF module could work over this distance across the concrete walls? Will any of the super-cheap ebay ones (433 MHz) work with a quarter-wavelength antenna attached (17cm I believe)? Or should I look at the xBee modules (but it seems an overkill)? Also, I believe the EU laws limit the power to 10mW for the 433 Mhz range and 25mW for the 868 range so I'd like to stay within the limits to be safe.
Thank you for your help in advance!