Wearable device with air quality sensor

A wearable device with an air quality sensor, the wearable device, comprising a housing enclosing an electronic board, a display arrangement, a battery, the housing lodging a cavity with an internal area, the cavity containing an air quality sensor in the internal area, the cavity being delimited by a cavity wall and by a membrane, the membrane having an inner wall oriented toward the cavity internal area and an outer wall opposed to the inner wall, the internal area of the cavity being in fluid communication with the ambient air through the membrane, the membrane being permeable to air and substantially not permeable to water.

FIELD OF THE DISCLOSURE

The present invention concerns a wearable device, like a wrist watch or an activity tracker, with an embedded air quality sensor. Here, the term ‘air quality sensor’ encompasses any sensor able to determine a concentration level of some chemical compound in the air which can have an impact on human health (otherwise called “pollutants”), among them for example NO2, O3, NOx, CO, SO2, and others, without excluding chemical components which can have a long term impact on mankind environment like CO2, O3, etc. . . . .

BACKGROUND OF THE DISCLOSURE

Recently, some have suggest to include an air quality sensor into a device like a wrist watch, as disclosed in documents US2014277624 and US2015238141. However, these attempts to include an air quality sensor into a wrist watch remain rather unrealistic proposals and/or exhibit a rather bulky configuration.

Furthermore, the attempts to embed an air quality into a wrist watch have not taken into account various everyday life environmental conditions to which the wrist watch (or ‘wearable device’) is submitted. For example, a wrist watch is exposed to water when the user washes or rinses his/her hands. Sometimes the user sweats and the surface of the watch adjacent to the skin may become wet or even dirty on the long run.

Also, a wrist watch is usually exposed to mechanical stress like shocks and free falls, and therefore, all the elements exposed to the outside must be rugged and solid.

Also, a wrist watch must remain in a size compatible with men and women size standards.

Also, many recently marketed multi-function watches or smart watches tend to have an insufficient energy autonomy, requiring frequent recharges or battery replacement(s).

Finally, it is desirable that the basis for air quality evaluation by the sensor should be substantially in real time, and thus the air sample subject to analysis shall be renewed frequently enough.

Therefore, there remains a need to provide a watch or a wearable device with an embedded air quality, robust and providing reliable measurements for the air quality, whatever the condition of use regarding the watch.

SUMMARY OF THE DISCLOSURE

According to one aspect of the present invention, it is disclosed a wearable device with an air quality sensor (2), the wearable device comprising a housing (100) enclosing an electronic board (16), a display arrangement (15), a battery (6), the housing lodging a cavity (1) with an internal area, the cavity containing an air quality sensor in the internal area, the cavity being delimited by a cavity wall and by a membrane (3), the membrane having an inner wall (30) oriented toward the cavity internal area and an outer wall (31) opposed to the inner wall, the internal area of the cavity being in fluid communication with the ambient air through the membrane, wherein the membrane being permeable to air and substantially not permeable to water.

It is to be noted that the wearable device is to be broadly construed. The wearable device can typically be a watch, a wrist watch or an activity tracker, without excluding other types of personal wearable devices (glasses, necklace, ring, etc. . . . ).

Thanks to these dispositions, the air quality sensor is protected inside the housing of the wearable device against damages. Namely, the wearable device can withstand shocks or falls without negative impact on performance. Particularly, the air quality sensor is perfectly protected inside the wearable device, whereas, at the same time, the sensor is able to sense various concentration of chemical compounds present in the air outside the wearable device, thanks to the fluid communication channel through the membrane which is permeable to air.

Furthermore, the user can for example immerse briefly his wrist wearing the watch (or generally wearable device) in water without damaging the sensor since the membrane forms a barrier against ingress of water.

Moreover, the arrangement of the sensor in the cavity of the housing enables to perform a reliable measurement of pollutants.

The wearable device can be used on one hand to detect pollutants in the general environment of the user, and on the other hand to detect some particular chemical species present in the breath of the user when the user exhales or blows toward the wearable device.

The term “display arrangement” should be here construed broadly. According to one embodiment, the display arrangement may comprise analog type indicators, namely with physical stick-like hands forming analog time display indicators and additionally an auxiliary hand to display a current amount of physical activity performed by the user wearing the watch. According to another embodiment, the display arrangement may comprise digitalized pixel area, able to display a large variety of items including virtual hands for time indication.

According to still another embodiment the display arrangement may comprise both a digitalized pixel area, and physical stick-like hands forming analog indicators (for time and other data).

In various embodiments of the invention, one may possibly have recourse in addition to one and/or other of the following arrangements.

According to one option, the internal area of the cavity (1) is in fluid communication with the ambient air exclusively through the membrane (3), the cavity being elsewhere tightly isolated from the inside of the housing (100). Thereby, possible polluting gazes that may come from the inside of the watch itself (e.g. from electronic component or battery or coating material) can be advantageously prevented.

According to one option, the housing (100) is formed by a main casing (4), a transparent cover (11) and a back cup (12), the main casing comprising at least one through bore (14) located in an perforated area (140) for fluid communication between the internal area of the housing and outside environment, the outer wall of the membrane (31) facing the perforated area. Thereby, the membrane is not exposed directly to the outside environment, the main casing offers mechanical protection together with fluid communication; air passage is enabled across the through bores toward the membrane, and further across the membrane toward the air quality sensor. Air renewable is sufficient for real-time analysis.

According to one option, the air quality sensor (2) is able to sense and determine the concentration of NO2 and O3. Such a dedicated focused sensor advantageously exhibits a small size and a very low electrical consumption.

According to one option, the air quality sensor (2) is able to sense and determine the concentration of CO and/or NO2 and/or SO2. Thereby, the concentration of most common air pollutants can be determined, and according to a further option reported wirelessly to mobile device of a user.

According to one option, the air quality sensor (2) includes an amperometric sensor with a power consumption below 5 micro-amps. Thereby, the lifetime of the battery can be substantially improved if compared with some other wearable devices including gas sensor(s).

According to one option, the air quality sensor (2) includes an amperometric sensor with a volume less than 0.2 cm3. Thereby, such sensor can be integrated in a standard watch volume, even in a standard women watch volume.

According to one option, when the wearable device is a watch, the cavity wall is delimited by a dial plate (13) and by the air quality sensor (2), the dial plate (13) defining a top portion and a side portion of the cavity wall, a bottom portion of the cavity wall being formed by the air quality sensor (2), the interface between the sensor (2) and the dial plate (13) being locally sealed, the cavity wall comprising on the side portion an opening (130) closed off by the membrane (3). Thereby, the dial plate provides an integrated solution to lodge the air quality sensor and to provide an air cavity. The bill of material and manufacturing process are thereby optimized.

According to one option, the interface between the sensor (2) and the dial plate (13) is sealed using at least one gasket (8).

Elastomeric gasket in a groove is a reliable solution to provide fluid tightness.

According to one option, there is provided a shoulder (131) formed in the dial plate (13) around the opening (130) from a surface of the dial plate opposed to the cavity wall, the membrane (3) being tightly received against the shoulder. It is therefore easy to glue or solder by ultrasonic vibrations the membrane on the shoulder so that it closes tightly the cavity and the border of the opening.

According to one option, there is provided an inner space (132) located between the membrane (3) and the perforated area (140), the inner space (132) being insulated from the inside of the housing (100) using a gasket (82) inserted between the housing (100) and the dial plate (13) close to the opening (130).

This allows to handle possible manufacturing play entailed by deviations of dimensions in an industrial process.

According to one option, the display arrangement may comprise a plurality of physical stick-like hands forming analog indicators and at least a digital display area. This kind of mixed solution advantageously enhances comfort and readability from the user standpoint.

According to one option, each through bore has typically a dimension comprised in the range 0.05 and 1.5 mm; a preferred range for the bore diameter is [0.5 mm, 1.5 mm]. Although the through bores can have any dimension, this particular range avoids a water meniscus which could obstruct the bore after exposition to water.

According to one option, the electronic board (16) comprises a hole (160), the size of the hole being adapted for receiving the air quality sensor through said hole, the sensor emerging from both sides of the electronic board.

We obtain therefrom an advantageous integration of the air sensor, a compact piling up of components, enabling a thin package and giving a low thickness of the watch.

The display arrangement may further comprise a multi-color indicator Led, whose color is controlled by the electronic board according to the sensed level of air pollutants in the sampled air; whereby the user can have a very simple feedback of the current air quality around him/her.

The watch may further comprise a vibrator, controlled by the electronic board which is configured to activate the vibrator in case the sensed level of pollutants exceeds a predefined threshold; whereby the user can be warned at any time, even though he/she does not look at his/her watch.

According to one option, the air quality sensor (2) may be able to determine the concentration of NO, and, whenever the user exhales towards the wearable device, the wearable device may be used to detect asthma, emphysema or similar lung disease from the breath of the user.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the figures, the same references denote identical or similar elements.

As illustrated onFIGS. 1 and 2, one exemplary embodiment of the present disclosure relates to a wrist watch9. The wrist watch in question exhibits a standard size suitable for both men and women. An example of such a device is a watch name “Activité™” from the present applicant “Withings™”. The body of the watch has preferably an external diameter D of 42 mm or less; the thickness E of the body is 14 mm or less. Preferably, the thickness E may be 12.5 mm or 12 mm.

From the body, there are provided projections41for attachment to a wristband19as known per se, thus not described in detail here.

The wrist watch9illustrated here is a digital watch, namely all the indications given on the front face of the watch are given by a high definition dot matrix display, of LED or OLED technology, which is referred to herein as display arrangement15.

Virtually, almost any object can be displayed using this type of display, pictograms, numbers, digitalized areas150. Also, virtual hands151,152(for hours and minutes display) can be displayed using such high definition display; there can be provided an auxiliary indicator153as well.

Alternately, the present invention can be applied to an analog type watch, that-is-to-say a watch where the time is indicated through a dial and solid stick-like hands (one for hours, one for minutes, and optionally one for seconds) driven by stepper motors and gear trains as known per se.

Alternately, the present invention can be used in a hybrid watch, having both solid stick-like hands and digitalized display area.

In a preferred illustrated embodiment, the body of the watch is substantially round; but in other embodiments, the body of the watch can be substantially square or rectangle.

As illustrated, particularly visible onFIG. 2, the exemplified watch comprises, from bottom to top:

a main casing4,

a back cup12,

a battery6,

a printed circuit board16and a sensory device2,

a dial plate13, otherwise called “dial support”,

a top cover11, which is transparent.

The vertical direction denoted X is defined as the direction transverse to the plane of the watch dial. The thickness of the watch is defined along this vertical direction X.

Further, there is also defined a longitudinal direction denoted Y, perpendicular to X and which corresponds to the main direction of extension of the wristband19from the watch. Further, a third direction, perpendicular to the other ones, is named “transversal” and denoted A. The plane A,Y is referred to as a watch plane.

According to the present disclosure, there is defined a housing100of the wrist watch9which includes the main casing4, the back cup12and the top cover11; the housing can also be called “enclosure” since it encloses and protects all the internal components and elements contained in the watch.

As illustrated onFIGS. 1 and 2, the main casing4comprises a cylindrical portion42having a vertical axis; the cylindrical portion42is prolonged downwards by a tapered frustoconical portion denoted43; the tapered portion is further prolonged downward by a flat ring portion44. The flat ring portion44is shaped as a disc with X axis, and comprises a large central opening45.

The main casing4is preferably manufactured in stainless steel; alternatively light alloy or high-performance plastics like ABS, or other robust plastic material, can also be considered.

The back cup12is formed like a cup with a bottom section inserted in the above mentioned central opening of the main casing. The bottom section is prolonged upwards by a tapered portion adjacent internally to the tapered frustoconical portion of the main casing.

The back cup12is manufactured from a plastic rigid material, for example ABS or polycarbonate.

Advantageously, the above-mentioned sensory device2is an air quality sensor2which is enclosed in the housing.

The air quality sensor2is used to determine the rate of pollutants in the air prevailing at the vicinity of the watch. It should be noted that the samples collected at the watch are not substantially different from the air that the user/wearer of the watch is breathing.

More precisely, the air quality sensor2is enclosed in a cavity1provided in the housing100.

The cavity1is delimited by a cavity wall and by a membrane3, which is advantageously porous. The cavity1is in fluid communication with the ambient air through the membrane3as this will be described in detail later.

In use, the air enters the housing of the watch100and passes across the membrane3. The pollution rate is measured by the sensor2in the internal area of the cavity1.

According to one first possibility, the air quality sensor2can be a sensor mainly reactive to NO2 (Nitrogen Dioxide). According to another possibility, the air quality sensor2can be a sensor mainly reactive to NO (Nitrogen Oxide).

According to another possibility, the air quality sensor2can be a sensor mainly reactive to SO2 (Sulfur Dioxide). According to another possibility, the air quality sensor2can be a sensor mainly reactive to CO (Carbon Monoxide).

According to another possibility, the air quality sensor2can be a sensor mainly reactive to H2S (Hydrogen Sulfide).

According to other possibilities, the air quality sensor2can be a sensor mainly reactive to CO2 (Carbon Dioxide) or a sensor mainly reactive to ozone (O3) or a sensor mainly reactive to chlorine or a sensor mainly reactive to benzene, or a sensor mainly reactive to methane.

According to another possibility, the air quality sensor2can be a sensor reactive to two or more of the above mentioned chemical compounds.

According to a preferred embodiment, the air quality sensor2is reactive both to NO2 and O3, with a higher gas selectivity than known general-purpose pollutants sensors, like for example the so-called VOC sensors.

The physics of the sensor(s) relies on electrochemical reactive process, with a chemical layer combined with a transducer like typically an amperometric sensor.

A working electrode (or catalyst) promotes a chemical reaction when in contact with the gas, which takes place with regard to a second electrode (common=counter electrode).

For example, respective chemical reaction for CO and NO2 are:
CO+H2O=CO2+2e−+2H+ (electrons are released in the working electrode)
NO2+2e−+2H+=NO+H2O (electrons are captured in the working electrode)

Chemical interaction velocity follows the Arhenius law with a certain activation energy E which depends on many parameters: Kc (speed)=A exp(−E/RT)

The kinetics of a given chemical reaction makes a corresponding sensor responding immediately to a certain gas and very slowly to another one.

A bias reference voltage is set to the working electrode which results in a current flowing from/to the working to the ground electrode, the current depending on the kinetics of the considered chemical reaction.

Electrolyte is provided between the two electrodes to transport the H+ ion from one electrode to the other electrode.

According to one exemplary choice, one can select product reference 3SP_NO2_20 from SPEC Sensors, LLC, of Newark, Calif. Advantageously, thanks to its fuel-cell like technology, the air quality sensor2exhibits a very low electrical consumption, namely an average consumption when powered less than 5 microAmps, preferably less than 2 microAmps.

If we consider additionally the polarisation current from the main PCB, the total amount of current used for the sensor is preferably less than 10 microAmps Therefore, with a conventional lithium battery6for a watch, for example of the type CR2025 or CR2032 (“button cell”), the lifetime of the battery can be advantageously more than one year, preferably around 18 months or even two years.

It should be noted that in one embodiment, even though the sensor is permanently supplied, the sampling of sensor signal is made from time to time to lower further the electrical consumption.

It is important to note that more than one sensor can could be arranged in the air cavity, for examples two sensors or more.

As shown onFIG. 5, the exemplified air quality sensor2is composed of three sections, one above the other along the vertical direction. The lower section denoted21is in form of a disc and has a circular periphery. The lower section houses an electrochemical cell comprising a reactant like an electrolyte or a gel.

The lower section is followed upwards by an intermediate section22, having a rectangular shape. The intermediate section22is a ring shaped thin PCB for electrical connection to the main printed circuit board16(soldering face-to-face).

A top portion23has also rectangular shape, but with smaller dimensions in the shown example. The top portion23forms a cover and comprises a recess24opened in the surface of the top portion to let the air enter the sensitive part below.

The largest section of the air quality sensor2exhibits dimensions in the plane A,Y of the watch, comprised between roughly (5 mm×5 mm) and (15 mm×15 mm), typically around 10 mm×10 mm.

A particular mechatronic integration solution will be explained further.

However, it should be noted that the geometric configuration of the air quality sensor2can be slightly different or completely different.

In the shown example, the cavity1is delimited by the dial plate13and by the air quality sensor2. The dial plate13defines a top portion137and a side portion136of the cavity wall. A bottom portion of the cavity wall is formed by the air quality sensor2itself.

The dial plate13is for example formed in polycarbonate. Although, various other plastic materials can be considered for the dial plate.

The dial plate13is illustrated onFIGS. 3aand 3bin the case of wrist watch housing with a circular shape. The dial plate is a disc with a peripheral rim134. The disc has a diameter slightly inferior to the internal diameter of the cylindrical portion42of the casing4.

The disc extends in the plane A,Y of the watch with a top side13A, in which the display arrangement15is arranged and a bottom side13B which faces the printed circuit board16.

A border133extends from the bottom side13B of the disc downwards in the vertical direction on a length inferior to the height of the peripheral edge from the bottom side of the disc. The border133delimits the cavity. The border133,136defines in this embodiment typically a rectangular shape.

The cavity has in this embodiment a square shape footprint with side size between 0.5 cm and 1.5 cm.

Alternatively the cavity could have a circular section.

The cavity1is closed by the sensor2at the bottom side of the cavity1. More precisely the sensor2surface22ais in contact with the lower end of the border133, and all along the periphery of the border133. It is possible to provide a glue or silicon bead to provide a tight junction.

Referring toFIGS. 1 and 4, the top section23protrudes slightly in the cavity1. The extremity of the border133opposed to the disc comprises in particular a groove138along the extremity of the border133.

A gasket81is for example inserted along this junction area between the sensor and the border133. The gasket81has for example a rectangular loop shape matching with the shape of the border of the cavity. The gasket81has for example a round cross-section, configured to be inserted in the above mentioned groove138.

The material of the gasket is chosen to be neutral versus the detection of chemical compounds; among the preferred materials are Viton™, EPDM (ethylene propylene diene monomers), or silicon.

In this embodiment the thickness of the air sensor is typically between 2 mm and 4 mm.

One side of the cavity wall formed by the border133is formed nearby the peripheral edge134of the disc in a way wherein there is a material continuity and the border133and the peripheral edge134are locally the same.

A tunnel17is open from the internal area of the cavity1through the cavity wall locally and then in continuity through the peripheral edge134, ending in an opening130at the surface of the peripheral edge134. The tunnel17connects the internal area of the cavity with the opening130.

The membrane3closes off the cavity wall opening. The membrane3is permeable to air and not permeable to water. The membrane3comprises a porous material.

The membrane3is formed as a thin wall manufactured in synthetic material having a microporous structure. Across the membrane, diffusion is governed by Fick's law.

Various materials are available to achieve water protection while allowing air passage. According to one example, the membrane is made of polytetrafluoroethylene (also called ™Teflon) marketed under ™Gore-Tex membranes. According to another example, the membrane can be made of non-woven high-density polyethylene fibers. Nanopores having a size comprised between 1 μm and 5 μm let the way for air molecules while retaining bubbles of water. The thickness of the membrane3is comprised between 50 μm and 500 μm.

The ‘Schmerber’ index, denoting water non-premeability performance, is at least 5 000; in other words, water cannot passes through the membrane for a pressure difference threshold up to 200 mbar. Preferably this pressure difference threshold is typically 270 mbar.

Likewise, IP rating of the membrane3is at least IP64, preferably IP67 or IP68.

Air permeability is at least 70 liter/hour/cm2at a 70 mbar of pressure difference.

An inner wall30of the membrane3is oriented toward the cavity internal area and an outer wall31is opposed to the inner wall. The internal area of the cavity is in fluid communication with the ambient air through the membrane3. A shoulder131is formed around the opening130.

In the plane of the peripheral edge134from the surface of the peripheral edge toward the cavity internal area. The membrane3is in this embodiment inserted in the shoulder131in a way wherein the membrane3is locally in the plane of the peripheral edge surface.

Alternatively the periphery of the inner wall30of the membrane can be welded with ultrasound to the surface of the peripheral edge134to close off the cavity.

The opening130has in this embodiment an oval shape extending along an axis parallel to the watch plane. So the membrane has a typical oval shape in this embodiment to be placed against the described shoulder.

Alternatively the opening can have a different shape, such as a rectangular shape.

In the illustrated case of a digital watch, any type of object can be displayed as mentioned above.

In the analog type variant, the top side13A of the dial plate13supports in this embodiment the physical pointers151,152of the watch for example.

The transparent cover11covers the pointers in a way wherein the pointers are visible through the transparent cover11.

The peripheral edge134on the top side of the dial plate13comprises a shoulder, as illustrated onFIG. 3c, adapted to insert the peripheral edge of the transparent cover11in a watertight way.

The dial plate13is enclosed in the housing such as that the disc is parallel to the plane of the watch. In this way wherein the peripheral edge134is parallel to the lateral part of the main casing10formed by the cylindrical part. The opening130faces the lateral part. The membrane3is thus parallel to the main casing locally.

The lateral part of the main casing10has a vertical extension comprised between 4 mm to 6 mm. The thickness of the watch is roughly the height of the main casing10which is in the range of 8 mm to 14 mm.

The main casing4is for example obtained from stamping in one piece of stainless steel. The lateral part of the main casing10comprises a perforated area140, wherein through bores14are open to connect the internal area of the housing100to outside.

The through bores14are typically aligned in the perforated area140, facing the opening130. There are for example six bores. Each bore14has a diameter comprised between 0.05 mm and 1.5 mm and typically of about 1 mm. The through bores14are separated by about 1.5 mm.

The internal area of the cavity1communicates with outside through the through bores14and through the membrane3. The air enters the housing100through the through bores14and then enters the cavity1through the membrane3.

The diameter of the through bore14is typically given proportionately to size of the cavity1to avoid a meniscus effect in particular. The oval opening130has a typical extension in a range of 1 cm to 1.5 cm and typically around 1.2 cm. Alternatively the bores could be replaced by a slit.

An inner space132, illustrated onFIG. 4, is in this embodiment located between the membrane3and the opening area140.

The housing100encloses several other items as an electronic board (PCB)16with a controller5, an oscillator, a battery6either conventional or rechargeable, etc . . . .

The battery of the watch is typically below the PCB inside the cavity in the bottom part of the housing. Gas is for example possibly emitted by the PCB or by the battery and could disturb the measurement by the sensor2.

As illustrated onFIG. 6, the PCB is positioned between the battery and the cavity, parallel to the plane of the watch. The PCB comprises a hole160in which is inserted the sensor3. In this configuration, the periphery of the bottom side of the intermediate portion is in contact with the PCB surface. The sensor extends through the PCB in a way wherein the bottom face of the air quality sensor is vertically below the PCB16.

In this configuration the thickness of the watch housing100is minimized with the integration of the air quality sensor through the PCB.

The sensor2is connected to a control unit5integrated to the PCB16which collects and treats air quality data. A diode155is for example mounted on the dial plate top face and connected to the control unit. The diode is used to provide for example a light color signal representative of the air quality measured.

As an alternative or complementarily the watch could be in wireless communication96with another device like a smartphone66, or other devices and the data could be displayed on the screen of the connected device as illustrated onFIG. 7.

Instead of a single led155, the small bargraph can be used.

Also, the actual sensed values of pollutants can be displayed on the digitalized area150.

On the smartphone66, there may be provided histograms of pollutant rate along the present day, along the past three days, along the past week etc. . . .

Additionally, there may be displayed for each pollutant compound, a threshold line showing the predefined alert level, with different colours on histograms whenever the pollutant rate become higher than the threshold(s).

Optionally, there may be provided one or more user actuator88otherwise called button; various purposes can be allocated to actuation of such button, as known per se.

In the analog type version, stepper motors and gear trains are arranged preferably on the side of the watch plane opposed to the side where the air quality sensor is placed.

Optionally, the watch is equipped with a photo plethysmograpic (PPG) sensor125used to sense the heart rate of the user of the watch. The PPG sensor is arranged on the bottom face of the watch.

Optionally, the watch is equipped with an electrode124in contact with the user's skin to form a sensor used for ECG analysis. The electrode for ECG sensing is also arranged on the bottom face of the watch.

Optionally, the watch is equipped with a temperature sensor126, configurable to measure the skin temperature on the wrist of the user. The skin temperature sensor is also arranged on the bottom face of the watch. There may be provided additionally an ambient temperature sensor.

Optionally, the watch is equipped with a vibrator, which can be used to notify the user with a particular message or a particular alert.

Regarding the predefined thresholds to trigger an alert, the following values can be taken into account.

For NO2, a first threshold value is set at 200 μg/m3.

For NO2, a second threshold value is set at 400 μg/m3.

Each of the first and second NO2thresholds are considered in conjunction with a minimum exposure time, for example an exposure duration or a certain number of times when the threshold is exceeded.

For O3, a first threshold value is set at 240 μg/m3.

For O3, a second threshold value is set at 300 μg/m3.

For O3, a third threshold value is set at 360 μg/m3.

Each of the first, second and third O3thresholds (abovementioned) are considered in conjunction with a minimum exposure time, for example an exposure duration or a certain number of times when the threshold is exceeded.

Once a particular threshold is exceeded with its associated time condition(s), a local message can be given by vibrations, and/or by a particular color on the indicative Led. Also, one or more messages can be sent immediately to the connected smart phone66.

As already stated, although the shown embodiment relates to a watch, the configuration of the membrane, the cavity and the air quality sensor can of course be applied to any kind of personal activity tracking device, or any kind of wearable device.

As already stated, the above configuration (for a watch or more generally for a wearable device) with the adequate amperometric gas sensor can also be used advantageously for breath analysis, when the user blows towards the wearable device. Preferably, the result can be faster when the user blows directly towards or into the bores14.

Breath analysis is a known technique to screen diseases. For example the presence of NO in the breath is a marker for asthma, emphysema or similar lung disease.