Blocked drain in kitchen (med)

Blocked Sewer Alarms for Small Businesses

As many of our customers will testify the damage and losses to a business caused by a clogged sewer, surcharge from a blocked sewer or overflow from a blocked sewers, drains or failed sump pump can be devastating.

Not only is there the cost of the damage but also there are the consequential losses such as loss of footfall and/or production which are often not covered by insurance policies.

BDT Sewer Level Transducer & Sentinel Alarm Receiver

Blocked Sewer Alarm System Installed

Blocked Sewer Alarm Systems Installed in Complex Sewer Access Chamber in London’s West End

The BDT is a simple and effective blocked sewer sensor based upon our award winning BDT sensor technology that won the SBWWI innovation award in 2012 and now in 2017 has notched up over 2.5 billion readings and messages broadcast!

The BDT is a fixed point level sewer sensor that the broadcasts the level within a sewer (high level or normal) at regular intervals using wireless technology to a receiver mounted nearby that raises and alarm if the sewer level rises due to a blockage, surcharge or high levels in sumps. With the advanced warning delivered by the system it is possible in many cases to prevent a blockage escalating into a major flooding disaster and also permits drainage teams to be called discretely out of hours to remove the blockage or to fix a blocked or failed sump pump.

Easy to Install:

The BDT is battery powered and communicates using wireless technology permitting it to be installed in drains and sewers without the need to slit floors to run cables etc. The unit is 100% waterproof, safe in the presence of sewer gases and resistant to corrosion.

The BDT is simply installed using a couple of screws just below the manhole cover of the sewer prone to blockage or sump. The BDT sensor is set just above the invert or in the case of a sump just above the high level limit using nothing more than a cable tie and the cover is replaced.

The Sentinel Alarm receiver is located on a wall nearby. The Sentinel Receiver is capable of monitoring up to 4-locations or alternatively provide multiple level warnings in a single or multiple drains and/or sumps. (High level 1 and High level 2, etc.).

The Sentinel Receiver constantly monitors the level status issued by the BDT sensors. In the level is normal a bright green Zone LED is illuminated and if the level is high the LED turns red and a sounder is activated.

There is also a small relay within the Sentinel Receiver that permits the alarm to be connected to an external telephone auto dialler or SMS text communicator.

Blocked sewer alarm system for small businesses

Fig 1: Blocked Sewer Alarm System for Small Businesses based upon the Sewer Sentinel Receiver and BDT  Wireless Blocked Sewer Alarm Transmitters


  • Blocked Drains for Car Parks
  • High Sump Alarm
  • Blocked Sump Pump Alarm
  • Clogged Sewer Alarm
  • Packet Sewage treatment Plant Alarm
  • Underground Car Parks
  • Factories
  • Office Blocks
  • Basements Flood Alarms
  • Blocked Sewer Alarms for Factories
Blocked Sewer Alarm System Installed in Car Park of Office Block

Blocked Sewer Alarm System Installed in Car Park of Office Block

Customer Profiles Include:

  • Schools & Playgroups
  • Restaurants
  • Nightclubs, Public Houses & Bars
  • Offices
  • Retail
  • Warehouses
  • Local Authorities

DIY Kits or Fully Installed

We are happy to supply DIY kits or to offer a comprehensive service from site survey through to installation and commissioning Please contact our sales department or your local agent for further details.

Sentinel Receiver  Sewer Sentinel 4-Zone Receiver Data Sheet


Q. How does the BDT measure the level?

A. It measures level of the sewage/water through analysis of the dielectric constant of  the media that surrounds its body.

Q. Is the BDT immune from ragging?

A. Yes due to its ability to swing in the flow it generally de-rags naturally. Further, the active area of the BDT is kept well away from the cable using extension tubes. Because the BDT acts on the “bulk dielectric principle” it also can ignore the presence of stuck leaves and tissue on its surface. The MKII BDT introduced in the summer of 2014 has a significantly improved immunity to FOG,

Q. Is the BDT technology proven?

A. The underlying dielectric measurement principle has been around for over 80-years, the BDT however has brought the technology into the 21stCentury. Currently there are many hundreds of BDT units in service and thanks to the hard work of our R&D department we now have the MKII BDT, which has been in service since 2013.

Q. Can a BDT cope with washing machine foam?

A. Yes unlike ultrasonics that can fail miserably, the BDT is designed to ignore foam and will not give false alarm.

Q. Can I use a BDT in shallow sewers/drains?

A. The BDT  is ideal for use in shallow drains as shallow as 250mm deep. The BDT doesn’t suffer from “near field dead zones” that prohibit the use of ultrasonics.

Q. Does a BDT require calibration?

A. No calibration is required the trip point is set at the receiver which operates using a “fuzzy logic” control strategy.

Q. How do we set up a BDT?

A. Setting up a BDT is very simple, in fact even simpler than a float switch. The BDT simply has to be hung at the desired trip level point. The BDT has the major advantage that unlike an ultrasonic where the beam is invisible, the BDT is clearly visible and hence can be set to a particular level simply by adjusting /coiling the support cable, etc.

Q. What software do I require?

A. Nothing at all, no field programming is required to install a BDT system they simply work out of the box.

Q. What about steps and other protrusions?

A. Unlike an ultrasonic the BDT will not give false alarms due to reflections from steps and shelves.

Q. What depth can a BDT operated?

A. BDT Lite is supplied with 4m cable lengths as standard. Extra long cabled versions can be supplied to special order up to 6m long.

Q. Do we need to enter the sewer/drain to fit a BDT?

A. The whole concept of the BDT was to avoid confined space entry. The whole BDT can be fitted from the surface providing standard precautions are taken concerning safety restraints for personnel, tools and gas detection, etc.

Q. Is an ATEX certified version of the BDT available?

A. The BDT  is Intrinsically Safe by design and available to order for Zone 2. Standard BDT are supplied for Zone 2 operation.

A. The typical BDT  has a projected battery life of over 10-years which has been verified by the battery manufacturers computations. This assumes normal UK (drainage) ambient conditions and a  2.5 second sampling rate. To date in 2017 we have not received a report of premature battery failure.

Q. Can the BDT cable be cut and re-joined?

A. Unfortunately not as it includes a foil barrier that cannot be easily re-joined.