Acoustic emission (AE) monitoring of an active waveguide (a steel tube with a granular backfill surround) installed through a slope can provide real-time warning of slope instability by quantifying increasing rates of movement (i.e. accelerations) in response to slope destabilizing effects. The technique can also quantify decelerations in movement in response to stabilizing effects (e.g. remediation or porewater pressure dissipation). This paper describes the AE monitoring approach and presents results from a field trial that compares AE measurements with continuous subsurface deformation measurements. The results demonstrate that AE monitoring provides continuous information on slope displacement rates with high temporal resolution. Case studies are presented where the AE technique is being used to monitor coastal slopes at Filey and Scarborough in North Yorkshire, UK, to inform continuing risk assessments for these slopes. The results demonstrate that the AE approach can successfully be used to monitor slopes with relatively deep shear surfaces (>14 m); however, they also show that potentially contaminating AE can be generated by groundwater flowing through the active waveguide from relatively high-permeability strata in response to rainfall events.