AquaAlert
A research prototype · Medical Devices 295623 · EEBE UPC

Catching dehydration in older adults before symptoms appear.

AquaAlert is a two-sensor system — a smart bottle and an ankle wearable — that combines salivary conductance with whole-body bioimpedance. The fusion yields a single hydration index, updated every few minutes, with tiered alerts to user and caregiver.

§ 01 · The problem

Thirst is a late signal — and in older adults, it is often missing entirely.

The osmoreceptor response that drives thirst weakens with age. Combined with reduced renal concentrating ability and lower total body water reserves, this leaves adults over 65 uniquely vulnerable to heat. By the time confusion or syncope brings them to an emergency room, the deficit is already advanced.

Existing smart bottles count sips. Existing wearables for athletes infer hydration from sweat — a signal that fades precisely in the population at risk. Neither approach measures the body itself.

"The first measurable physiological change in mild dehydration is a rise in salivary electrolyte concentration. The first behavioural signal is fatigue. Thirst comes last."

AquaAlert moves the measurement upstream of symptoms by reading two biomarkers directly: salivary ionic conductance at the mouthpiece, and total body water through tetrapolar ankle bioimpedance. Both have prior validation against clinical reference methods.

Population at risk
9.0 million adults aged 65+ in Spain (INE, 2024).
Excess mortality
3,824 heat-attributable deaths summer 2024; 87% in the 65+ cohort.
Existing tools
Sweat patches (Nix, Epicore, hDrop) target athletes; clinical hydration assessment requires lab serum osmolality.
§ 02 · The system

Two devices. One index. Both passive to the user.

The bottle acts as BLE hub and gateway; the ankle mesh streams to it. A multimodal model fuses the four channels into a single 0–100 score and decides whether to nudge the user, page the caregiver, or escalate further.

AquaAlert Bottle Salivary conductance + thermal
AquaAlert Leg Mesh Tetrapolar ankle BIA
Primary sensor
Au coplanar IDE, 100 µm pitch, AC excitation
4-electrode Ag/AgCl, 50 kHz drive (AD5941)
Secondary sensor
NTC × 2 (liquid + ambient)
Skin-temperature thermistor
Radio
BLE 5.0 (acts as hub)
BLE 5.0 to bottle hub
Power
Li-Po 500 mAh, USB-C
Coin cell, ≈ 6-month life
Ingress / form
IP67, dishwasher-rated insert
Washable soft mesh, ankle
Target unit price
€50
€30
§ 03 · From signal to alert

A four-step pipeline. No cloud lock-in. No opaque inference.

  1. Acquisition

    Conductance is sampled at the mouthpiece each time the user drinks; ankle impedance is sampled every 30 minutes; temperatures continuously. Raw ADC values are stamped and buffered on the device.

  2. Fusion at the edge

    The bottle hub merges its own stream with the leg mesh over BLE GATT. No data leaves the device unless an alert is triggered.

  3. Index calculation

    A weighted model returns a 0–100 hydration score. The weighting was derived from the cited validation studies; it can be retrained per-user with three days of baseline measurements.

  4. Tiered notification

    Index ≥ 60: silent. 30–59: gentle prompt to drink, with the bottle's haptic vibration. < 30: caregiver notification and, if configured, a call to emergency contact.

§ 04 · Evidence base

Both modalities have been validated independently. AquaAlert combines them.

  1. Lu, Y. et al. Portable salivary diagnostic system for dehydration based on Au coplanar electrodes. Scientific Reports 9, 14771 (2019). Sample volumes 50–500 µL; sensitivity / specificity vs serum osmolality.
    86 / 91%sens / spec
  2. PMC clinical study (N = 20, 13 h). Salivary conductivity rose under 13-hour water restriction and fell after 1,000 mL rehydration; correlated with urinary osmolality, thirst scale, and body-weight loss.
    N = 20in-vivo
  3. Dasgupta, A. et al. Tetrapolar ankle bioimpedance at 50 kHz vs reference total body water (2018). High correlation supports the wearable form factor.
    R = 0.97vs gold std.
  4. Ekingen, T. et al. Age-related decline in body water (2022), N = 242. Establishes the 65+ cohort as the principal risk group for hypohydration during heat stress.
    65+primary cohort
§ 05 · Where this sits

A category the wearables industry has skipped.

The hydration-monitoring market is growing, but the products are designed for athletes and industrial workers. None target the elderly. None are designed for institutional procurement. The market gap is not technological — it is one of attention.

Product Target user Body-state sensing Caregiver alerts Reusable Institutional channel
AquaAlert Adults 65+ Saliva + BIA Yes Yes Designed for it
Nix Biosensors Endurance athletes Sweat No Single-use patch No
hDrop Endurance athletes Sweat No Yes No
Epicore Biosystems Industrial workers Sweat No Single-use patch B2B industrial only
Kenzen Industrial workers HR + skin temp No Yes B2B industrial only
9.0M
adults aged 65+ in Spain — the principal risk cohort during heat events.
€312M
global hydration-monitoring market in 2024.
14.2%
projected CAGR through 2033.

The natural buyers are not individuals but institutions: regional health departments running summer heat-wave plans, residential care providers managing duty-of-care obligations, and mutuas integrating prevention into their service offering. Each has the budget, the mandate, and the distribution.

  • AyuntamientosPlan calor
  • Residencias de mayoresDuty of care
  • MutuasPrevention services
  • Salud públicaPopulation programmes

The demo simulates an afternoon with Antonio — 72, Barcelona — wearing the system through a heat warning. It runs in your browser.

No sign-up. No installation. The same interface the family would see on a phone, and the same caregiver console a residencia nurse would use.

Open the demo