XBee Series 1 module (chip antenna)

XBee RF Module S1

CIP ANTENNA MODULE, XBEE, 1mW

Long Range Data Integrity, Low Power, Advanced Networking & Security, ADC and I/O Line Support

XBee Series 1 (also called XBee 802.15.4)
These are the easiest to work with, they don’t need to be configured, although they can benefit from it. Because they are easy to work with we recommend these especially if you are just starting out. For point to point communication these modules work as well as the Series 2 but without all the work. A Series 1 module won’t say Series 1 on it, but it also won’t say Series 2. If it doesn’t say then your module is a Series 1. Series 1 and Series 2/2.5/ZB hardware are NOT compatible. Don’t try to mix and match, don’t even think about it, it won’t work, not even close. Nope, stop thinking about it…! 

Datasheet