Here's an explanation:
Geiger-Muëller Detector
The Geiger-Muëller (GM) probe is the most common radiation detection instrument on campus. In this meter, radiation detection causes both visual and audio responses. The meter detects radiation events and does not differentiate types of energies or radiation. The GM does is only used to detect radiation and does not measure radiation dose. The most common GM is a Pancake Probe, as shown below with a survey meter.
The GM probe has a thin 'window' at one end that is very fragile. This probe is used for detecting beta emitters (e.g. 32P, 35S, and 14C).

From the second site:
The SBS probe is designed to monitor floors and surfaces for beta contamination.
It consists of five mica thin-window Geiger Müeller detectors, a high-voltage power supply and pulse shaping electronics.

It can be connected to MIP 21A, CAB, MIP 10A and ECM 21 with the appropriate cable