Advice correct sensor(s) to detect person presence in a "relax" room

Hello,

our company has several relaxation rooms where folks can come and have a moment of peace. Unfortunately the same folks often forget to untag the room as occupied so much so that the local workforce has learned to ignore the red occupied sign completely.

Being an arduino beginner I realized that this situation may be solved by some form of arduino project.

My research however lead to much uncertainty which sensing method should be used.

The rooms are multipurpose - folks can exercise there on a mat, be sleeping on an armchair, or be changing their apparel inside a 3mx4m rooms. They may be in a complete dark, or very bright light...

I would like to ask for an expert advice on how to solve this problem as I do not think this is trivial case of IR or motion detector sensor. Folks can be standing, laying on teh floor, or be in the armshair, so I do not see a one sensor that would possibly reliably detect these cases. And false positives must be avoided at all cost.

If given tips of which sensor(s) to use, I think I can take it from there (at least by googling the right usages of the sensor(s) etc.). I just feel too inexperienced to properly weight the various sensor types against this usage case.

Any help, tips or nudge is highly appreciated.

Thanks!

Rather than ponder which sensors to purchase I would suggest looking at what parameters are available to measure first.
Consider a small room which may contain some or no furniture or fittings and that this may change over time.
This suggests to me that a differential measurement is required i.e. room without person as compared to room with person.
So, what changes occur when a person enters the room.
I see three measurable parameters.

  1. Every human exhales CO2 as about 4-5% of total gas volume. This occurs regardless of whether the person is active or snoozing in a chair, so maybe a CO2 gas sensor
  2. All human bodies generate heat so the presence of a body in the room will increase the room temperature, a temperature measurement may work.
  3. The hardest one! is to measure the increased weight on the floor.

All suggestions will probably produce microscopic changes so a differential measurement would be how I would tackle the issue.

I'm sure there are sensors that can handle the above measurements but I think deciding which parameters are easily and/or economically measurable would be a first step.

Overthinking…

A simple door latch with indicator is the correct technology for this, just like for a toilet, people
understand them, they are readily obtainable. You can’t forget to unlatch a door before leaving
a room.

MarkT:
Overthinking...

A simple door latch with indicator is the correct technology for this, just like for a toilet, people
understand them, they are readily obtainable. You can't forget to unlatch a door before leaving
a room.

Medical reasons why people inside can't latch themselves. But thanks for the suggestion anyway!

BanditDave:
Rather than ponder which sensors to purchase I would suggest looking at what parameters are available to measure first.
Consider a small room which may contain some or no furniture or fittings and that this may change over time.
This suggests to me that a differential measurement is required i.e. room without person as compared to room with person.
So, what changes occur when a person enters the room.
I see three measurable parameters.

  1. Every human exhales CO2 as about 4-5% of total gas volume. This occurs regardless of whether the person is active or snoozing in a chair, so maybe a CO2 gas sensor
  2. All human bodies generate heat so the presence of a body in the room will increase the room temperature, a temperature measurement may work.
  3. The hardest one! is to measure the increased weight on the floor.

All suggestions will probably produce microscopic changes so a differential measurement would be how I would tackle the issue.

I’m sure there are sensors that can handle the above measurements but I think deciding which parameters are easily and/or economically measurable would be a first step.

      1. room has aircon inside, with unstable function pattern. Not sure if these solutions would work on microscopic changes level.
  1. Yeah, had that one, but sadly impossible to implement.

I thought about IR map or IFR sensor, but unsure about the size of the room and sleeping people.

Not easy one this one eh?

I remember, 20+ years ago were ultrasonic sensors very popular. They worked slightly different than common HC SR-04, analogous by nature, sensor continuously radiated ultrasonic wave and monitor reflections. Any object introduced into space, distorts reflection pattern, and consequently triggers alarm.

Kovir_Wyttcliff:

      1. room has aircon inside, with unstable function pattern. Not sure if these solutions would work on microscopic changes level.
  1. Yeah, had that one, but sadly impossible to implement.

I thought about IR map or IFR sensor, but unsure about the size of the room and sleeping people.

Not easy one this one eh?

You have got an interesting project and aircon certainly presents some challenges.
My next suggestion is some form of RFID technology.
Each person could have a unique code or even all have the same code if privacy was an issue.
The RFID reader within the room would need to detect a tag presence to determine if the room was occupied.

This cheap thermal camera can detect people in a room, (with the appropriate software).

There are three ways you can do it

  1. Use a PIR sensor module to detect any movement inside the room

  2. You can use a load cell or piezo electric transducers connected to chair to detect an increased weight

  3. You can use Hall effect sensors or magnetometers in the doors, these are magnetic sensors which triggers when the like poles comes in contact with each other

I like the Panasonic Grid Eye sensor for this job. Unlike a PIR which senses movement, this can reliably detect a person who is not moving.

But there must be a zillion other ways to do it, all searchable on Google.

Heat is probably the best measure.

The heat of a person is not exactly microscopic - person acts as a 100-200W heater, depending on the level of exercise. Even at rest it's easily 100W of heating. A/C units will switch on noticeably more frequent.

Detection using one or a few IR cameras is probably the most reliable way, as long as you don't make them look too much like cameras (those using the room to change their clothes will not like the idea of being watched, or they probably wouldn't bother going to such a room in the first place).

People also emit quite some moisture (mostly sweat and breath), that may also be detectable.