Monitoring dependent individuals

1. A wearable child-monitoring system, comprising:

a wearable smart band associated with a monitored person, the wearable smart band comprising:

a band configured to secure the wearable smart band to a monitored person's body;

a battery;

a sensor configured to indicate whether the band has been removed from the monitored person's body;

a microprocessor; and

a radio configured to broadcast a radio-frequency signal, the radio-frequency signal encoding broadcast content with Gaussian frequency shift modulation;

a tangible non-transitory machine readable media storing instructions that when executed by one or more processors of a smartphone effectuate operations comprising:

receiving a first instance of the radio-frequency signal broadcast from the wearable smart band;

determining a perceived signal strength of the first instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a first value from broadcast content of the first instance of the radio-frequency signal;

determining that the monitored person is further than a first threshold distance from the smartphone based on both the perceived signal strength of the first instance of the radio-frequency signal broadcast from the wearable smart band and the first value obtained from broadcast content of the first instance of the radio-frequency signal;

in response to the determination that the monitored person is further than the first threshold distance, causing the smartphone to emit a first alarm;

receiving a second instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a second value from broadcast content of the second instance of the radio-frequency signal, the second value indicating an output of the sensor configured to indicate whether the band has been removed; and

in response to the second value, causing the smartphone to emit a second alarm, wherein:

the first value indicates a first vector of movement by the wearable smart band;

determining that the monitored person is further than the first threshold distance is based on the first vector;

the wearable smart band comprises a first inertial measurement unit (IMU) configured to sense the first vector;

the operations comprise:

obtaining a second vector of movement of the smartphone from a second IMU of the smartphone; and

determining a difference between the first vector of movement by the wearable smart band and the second vector of movement of the smartphone; and

determining that the monitored person is further than the first threshold distance is based on the difference between the first vector of movement by the wearable smart band and the second vector of movement of the smartphone.

2. The system of claim 1 , wherein:

the wearable smart band comprises a water-immersion sensor;

the operations comprise:

receiving a third instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a third value from broadcast content of the third instance of the radio-frequency signal, the third value indicating a reading by the water-immersion sensor; and

in response to the third value, causing the smartphone to emit a third alarm.

3. The system of claim 1 , wherein determining that the monitored person is further than the first threshold distance is based on the difference between the first vector of movement by the wearable smart band and the second vector of movement of the smartphone comprises:

combining a signal strength-based distance and an IMU-based distance.

4. The system of claim 1 , the operations comprising:

determining, based on a perceived signal strength of an third instance of the radio-frequency signal at the smartphone, that the wearable smart band is within a threshold distance of the smartphone and, in response, calibrating an IMU integral of the smartphone, the wearable smart band, or both.

5. The system of claim 1 , wherein the perceived signal strength is based on a Received Signal Strength Indication.

6. The system of claim 1 , wherein:

the radio is configured to periodically broadcast the radio-frequency signal as a beacon; and

the operations comprise:

determining that a third instance of the radio-frequency signal broadcast from the wearable smart band has not been received; and

in response to determining that the third instance of the radio-frequency signal broadcast from the wearable smart band has not been received, causing the smartphone to emit a third alarm.

7. The system of claim 1 , wherein:

the wearable smart band is configured to adjust broadcast strength of the radio-frequency signal based on distance from the smartphone.

8. The system of claim 1 , wherein:

the first value indicates a broadcast signal strength of the first instance of the radio frequency signal.

9. The system of claim 1 , wherein:

the wearable smart band comprises an accelerometer; and

the operations comprise:

receiving a fourth signal indicative of an impact sensed by the accelerometer of the wearable smart band; and

presenting information to a user of the smartphone in response to the impact.

10. The system of claim 1 , wherein:

the first value is a value that distinguishes radio-frequency signals of the wearable smart band from radio-frequency signals of other devices transmitting in range of the smartphone.

11. The system of claim 1 , wherein:

the wearable smart band comprises means for reducing power consumption.

12. The system of claim 1 , wherein the operations comprise:

presenting a third alert with the smartphone by vibrating the smartphone in response to determining that the third alert is of a first level; and

presenting a fourth alert with the smartphone by emitting an audible alert with the smartphone in response to determining that the fourth alert is of a second level, different from the first level.

13. The system of claim 12 , wherein:

the third alert corresponds to a second threshold distance between the wearable smart band and the smartphone;

the fourth alert corresponds to a third threshold distance between the wearable smart band and the smartphone; and

the third threshold distance is further than the second threshold distance.

14. The system of claim 1 , wherein:

the wearable smart band is configured to emit an ultrasonic signal; and

the operations comprise receiving the ultrasonic signal with the smartphone and inferring a distance based on the ultrasonic signal.

15. The system of claim 1 , wherein:

the wearable smart band comprises a pulse oximeter; and

the operations comprise:

receiving a third instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a third value from broadcast content of the third instance of the radio-frequency signal, the third value indicating an output of the pulse oximeter; and

in response to the third value, causing the smartphone to emit a third alarm.

16. A wearable child-monitoring system, comprising:

a wearable smart band associated with a monitored person, the wearable smart band comprising:

a band configured to secure the wearable smart band to a monitored person's body;

a battery;

a sensor configured to indicate whether the band has been removed from the monitored person's body;

a microprocessor; and

a radio configured to broadcast a radio-frequency signal, the radio-frequency signal encoding broadcast content with Gaussian frequency shift modulation;

a tangible non-transitory machine readable media storing instructions that when executed by one or more processors of a smartphone effectuate operations comprising:

receiving a first instance of the radio-frequency signal broadcast from the wearable smart band;

determining a perceived signal strength of the first instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a first value from broadcast content of the first instance of the radio-frequency signal;

determining that the monitored person is further than a first threshold distance from the smartphone based on both the perceived signal strength of the first instance of the radio-frequency signal broadcast from the wearable smart band and the first value obtained from broadcast content of the first instance of the radio-frequency signal;

in response to the determination that the monitored person is further than the first threshold distance, causing the smartphone to emit a first alarm;

receiving a second instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a second value from broadcast content of the second instance of the radio-frequency signal, the second value indicating an output of the sensor configured to indicate whether the band has been removed; and

in response to the second value, causing the smartphone to emit a second alarm, wherein the operations comprise:

inferring that the wearable smart band is within a second threshold distance of the smartphone; and

in response to the inference, adjusting an integral of inertial-measurement unit readings to reduce an effect of drift in determining that the monitored person is further than the first threshold distance from the smartphone.

17. The system of claim 16 , wherein:

the wearable smart band comprises a water-immersion sensor;

the operations comprise:

receiving a third instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a third value from broadcast content of the third instance of the radio-frequency signal, the third value indicating a reading by the water-immersion sensor; and

in response to the third value, causing the smartphone to emit a third alarm.

18. The system of claim 16 , wherein:

the first value indicates a first vector of movement by the wearable smart band;

determining that the monitored person is further than the first threshold distance is based on the first vector.

19. The system of claim 16 , wherein determining that the monitored person is further than the first threshold distance is based on the difference between the first vector of movement by the wearable smart band and the second vector of movement of the smartphone comprises:

combining a signal strength-based distance and an IMU-based distance.

20. The system of claim 16 , the operations comprising:

determining, based on a perceived signal strength of an third instance of the radio-frequency signal at the smartphone, that the wearable smart band is within a threshold distance of the smartphone and, in response, calibrating an IMU integral of the smartphone, the wearable smart band, or both.

21. The system of claim 16 , wherein the perceived signal strength is based on a Received Signal Strength Indication.

22. The system of claim 16 , wherein:

the radio is configured to periodically broadcast the radio-frequency signal as a beacon; and

the operations comprise:

determining that a third instance of the radio-frequency signal broadcast from the wearable smart band has not been received; and

in response to determining that the third instance of the radio-frequency signal broadcast from the wearable smart band has not been received, causing the smartphone to emit a third alarm.

23. The system of claim 16 , wherein:

the wearable smart band is configured to adjust broadcast strength of the radio-frequency signal based on distance from the smartphone.

24. The system of claim 16 , wherein:

the first value indicates a broadcast signal strength of the first instance of the radio frequency signal.

25. The system of claim 16 , wherein:

the wearable smart band comprises an accelerometer; and

the operations comprise:

receiving a fourth signal indicative of an impact sensed by the accelerometer of the wearable smart band; and

presenting information to a user of the smartphone in response to the impact.

26. The system of claim 16 , wherein:

the first value is a value that distinguishes radio-frequency signals of the wearable smart band from radio-frequency signals of other devices transmitting in range of the smartphone.

27. The system of claim 16 , wherein:

the wearable smart band comprises means for reducing power consumption.

28. The system of claim 16 , wherein the operations comprise:

presenting a third alert with the smartphone by vibrating the smartphone in response to determining that the third alert is of a first level; and

presenting a fourth alert with the smartphone by emitting an audible alert with the smartphone in response to determining that the fourth alert is of a second level, different from the first level.

29. The system of claim 28 , wherein:

the third alert corresponds to a second threshold distance between the wearable smart band and the smartphone;

the fourth alert corresponds to a third threshold distance between the wearable smart band and the smartphone; and

the third threshold distance is further than the second threshold distance.

30. The system of claim 16 , wherein:

the wearable smart band is configured to emit an ultrasonic signal; and

the operations comprise receiving the ultrasonic signal with the smartphone and inferring a distance based on the ultrasonic signal.

31. The system of claim 16 , wherein:

the wearable smart band comprises a pulse oximeter; and

the operations comprise:

receiving a third instance of the radio-frequency signal broadcast from the wearable smart band;

obtaining a third value from broadcast content of the third instance of the radio-frequency signal, the third value indicating an output of the pulse oximeter; and

in response to the third value, causing the smartphone to emit a third alarm.