The Sleep Sentry® Monitor

An aid for detecting nighttime hypoglycemia
by John Walsh, PA, CDE

Note:The Sleep Sentry is FDA approved and now available.

Visit Diabetes Sentry Products' web site. Read customer testimonials about the Sleep Sentry

The Sleep Sentry for diabetes
Designed over 20 years ago by Teledyne Avionics to detect nighttime lows, the original Sleep Sentry quickly fell on hard times. Despite being an excellent product with thousands of loyal users, it was ahead of its time and marketing faltered. Teledyne sold its remaining stock along with the rights to a Houston endocrinologist, Dr. Eric Orzeck, in 1983. The last of the original stock was gone by 1992, but after 10 years and a total redesign, the Sentry is again available.

Unlike devices such as the GlucoWatch , the battery-powered Sleep Sentry does not measure low blood sugars directly. Instead, it monitors for two symptoms of hypoglycemia: perspiration and a drop in skin temperature. The presence of either sweating or a two degree Fahrenheit drop in body temperature triggers an audible alarm that will awaken most people.

Unlike the GlucoWatch which has to be moved daily to prevent skin irritation, no problems are encountered with the Sentry which can be worn like a watch in the same location every night. Some users even wear it during the day, although adaptations such as wearing long sleeve shirts in cool weather or wearing it on the ankle under a sock help reduce false alarms. The Sentry even makes a good backup for those wearing a GlucoWatch in that it clearly signals when sweating occurs.

The Sleep Sentry costs $389 and has no additional costs (AutoSensors for the GlucoWatch cost $8 to $10 for each 13 hours of use. The Sleep Sentry takes 3 of the 357 batteries available at Radio Shack. They need replacing about every 6 months. DO NOT use Energizer batteries. Use Duracell or Varta.) The cost of the Sleep Sentry may be reimbursed by health insurance up to 75 or 80%.

For children, Children With Diabetes did not find the Sleep Sentry useful due to frequent false alarms in some sleep-active youngsters. But for certain parents who spend their nights worrying about their child, this device can be a great relief and improve sleep time. In our experience it is extremely useful for adults who experience severe or frequent lows. Some people with hypoglycemia unawareness may not begin to sweat or have a temperature drop before they enter a very limited state of consciousness. For these individuals, the problem of hypoglycemia unawareness may need to be solved before the Sleep Sentry will really be of benefit to them (see below).

I used the original Sleep Sentry in the early 1980's when I was developing my early concepts for blood glucose control and found it very helpful in detecting nighttime low blood sugars. In my experience, about half the alarms were actually lows. False alarms can be caused by normal sweating, or when the arm with the Sentry on it is moved from the warmth of blankets into the cool night air. Monitoring is increased by this divide, but the advantage is sound sleep and earlier detection of lows.

When the Sentry alarm sounds, the alarm has to be verified by testing with a blood glucose monitor. People often believe they always wake up when they are low, but a lot of research with continuous monitors has shown people wake up less than half the time when low. Most night lows go undetected and some of these can have serious consequences. A very common cause for hypoglycemia unawareness is having frequent nighttime lows which often go undetected.

The Sleep Sentry can be a good diagnostic aid when trying to adjust insulin doses to prevent lows. By keeping track of the times at which the Sentry alarm is triggered, it becomes easier to identify the insulin dose or basal rates that need to be changed to prevent these lows. I recently used the Sentry device when I was experiencing night lows but did not know when these lows were starting. I could have tested once or twice a night for several nights to find out. Instead, I wore the Sentry and over three nights I found the lows were starting earlier than I had expected, shortly after midnight. A quick resetting of basals corrected this problem. A similar correction can be done with injections if you give the precise timing of the lows to your physician.

Who Is It For? Ask yourself:
The Sleep Sentry is ideal for those who experience severe or frequent lows, those who live alone with their diabetes, and those who travel frequently. It also helps people whose daily activity varies greatly during the day, which makes precise insulin dosing difficult and increases the likelihood of night lows. Although it should never replace testing with a meter and should never be thought of as a way to avoid lows, it can provide some additional safety, such as while driving.
  • Have you ever had a severe episode of Hypoglycemia while sleeping?
  • What symptoms do you exhibit when you are low?
  • Do you ever set an alarm clock at night to do a blood test, for fear of going low?
  • Is your diabetic specialist aware of your interest in the Sleep Sentry?
  • Are you aware of the false positives associated with the Sleep Sentry monitoring program?

The sweating and skin temperature drop detected by the Sleep Sentry are both triggered when stress hormones are released, so the ability to release stress hormones is critical to its success. Some people with severe hypoglycemia unawareness may not release sufficient amounts of stress hormones to trigger an alarm in the Sentry until the reaction is quite severe. For these individuals, lowering insulin doses and a strict avoidance of low blood sugars for three to four weeks will be required before enough stress hormone response is available to cause the Sentry to alarm. If you go low on a Sleep Sentry but it does not alarm, taking steps to avoid all lows for a period of time would be wise.

The Sleep Sentry is not perfect. It will not alarm if it is not turned on, and it may not awaken someone who sleeps soundly, nor will it be acceptable for those who expect every alarm that sounds in the night to be a real low blood sugar. If you or your significant other have trouble going back to sleep when you awaken at night, it may not be wise to use this device. For others, an early hypoglycemia alarm that allows stress hormone release to be shut off faster may enable them to return to sleep faster.

Summary

Although the best treatment for lows is to prevent them, this is not always possible. The Sleep Sentry provides a great solution for those who want good control but are concerned about going to bed with normal readings. For many individuals, it is a great way to prevent unnecessary paramedic visits and nighttime lows.

Tips On Using The Sleep Sentry
  • If the velcro strap is too long, cut it to reduce the chance of it becoming dislodged during the night.
  • Always test when the alarm sounds. The Sentry can pick up a low even though you feel OK.
  • Some use the Sentry during the daytime as well, especially when the temperature is not overly warm. Long-time user Jerry Munden places it around his ankle under a sock to reduce false alarms due to temperature drops. (Caution: those with peripheral neuropathy may have reduced sweating in this location and get no alarm here!)
  • If glucose testing shows an alarm is false, Jerry suggests tuning the Sentry off, waiting a minute or two, then turning it back on. If the trigger for the false alarm was a drop in temperature, the Sentry will not alarm again. If it alarms again within a few seconds, then sweating is the cause for the false alarm.