HM Digital PM-2 External In-Line TDS Purity Monitor - Alarm Alert with Display 891144000045 but they serve different households:

but they serve different households:

Featuring a platinum sensing element and a double junction Ag/AgCl gel-filled reference

a conical tip for use with semi solids with a screw on cap to ensure proper storage

Compatibility: Santevia Gravity Water System (countertop and dispenser models)

HM Digital PM-2 External In-Line TDS Purity Monitor - Alarm Alert with Display 891144000045 but they serve different households:An ideal monitor alert for water coolers and other enclosed water purification systems. Alerts a user when the filtration system requires service. FEATURES External single line internal TDS monitor that is ideal for most water purification systems. Includes a light and optional alarm that alerts the user service is required when the TDS level reaches the pre programmed set point. User defined set points (any even number between 2 and 200).