Looks like a Smoke Detector!
The HyperGain RE08P series is a very compact round WiFi patch antenna providing 8 dBi gain with very broad coverage. It is suitable for indoor applications in the 2.4GHz ISM band, including IEEE 802.11b, 802.11g and 802.11n, and public wireless hotspot applications. This antenna is lightweight and features an aesthetic UV-stable, UL flame rated white plastic radome which can also be painted to match the room or building structure. Similar to the features of the HG2408P series, the RE08P series antennas feature 4 feet of low-loss coax cable enabling them to be directly connected to a radio connection without the additional expense of a pigtail cable. The RE08P can be installed for horizontal or vertical polarization and can be mounted flat against the wall or ceiling. Its unique design allows the cable to exit out of the side or from the back of the unit which is ideal for mounting in locations that require the cable to be hidden. In addition, optional mounting brackets are available for this antenna.