If you have a 5881 series wireless receiver and you want to add two-way functionality then the Ademco 5800TM Transceiver is what you'll want to buy. This will let you use any of Honeywell's bi-directional 5800 series devices.
There is no programming require to use this module. It is plug and play. If you have any of the RF style keypads then you will not need this module as the RF keypads have a TM module built into them.
Physical: 2-1/4 W x 4-1/8 H x 7/8 D (57mm x 105mm x 22mm)
Electrical: Voltage: +12VDC (from control panel remote keypad connection points)