# A Review of Medication Adherence Monitoring Technologies +
## 4 A Review of Medication Adherence Monitoring Systems
### Sensor-Based Systems
#### 4.1.2 Wearable Sensors  
In the recent years, Inertial Measurement Units (IMU) have seen rapid achievements from both the cost and intelligence points of view [105]. IMUs usually consist of accelerometers, gyroscopes, and magnetometers, or a combination of these [106; 107]. They have been widely used in healthcare applications by sensing motion and tracking individuals [108]. Ultimately, the usage of motion sensors can help in revealing possible information about individual's health [104]. In this part, we present many wearable sensing systems for medication adherence monitoring and place them in two categories, depending on the placement location of the body, neck-worn and wrist-worn. * _Neck-Worn Sensors_: In one of the studies [64], the authors propose a wearable system for detecting user adherence to medication up to the level of determining if the medication has been ingested. They built a pendant-style necklace that includes a piezoelectric sensor, a Radio Frequency (RF) board, and battery. The piezoelectric sensor is used for sensing the mechanical stress resulting from skin motion during pill swallowing and generating voltage as a response. Acquired data is sent via Bluetooth to a mobile phone that runs classification algorithms where they are analyzed further. Data collected from a population of 20 subjects were used to train and test the proposed system and a Bayesian-Network classifier was used for classifying the data received from the smart necklace. The achieved precision and recall for capsule were 87.09% and 90%, respectively. It is worth mentioning that another step that is used in this system is a commercial smart pill [109]. Major challenges associated with this approach pertain to user comfort and social acceptance [110] as the necklace needs to be worn by the patient and must be fastened and placed in contact with the skin during dose swallowing. Another tool for assessing medication intake is using acoustic sensors in the form of neck wearables. Such an approach has been utilized for food intake monitoring applications [111]. Although this approach requires further research, it shows promise for being applicable to medication monitoring [112]. In general, acoustic-based approaches focus on collecting acoustic data resulting from swallowing or ingestion activity with a microphone placed by the throat and then harnessing specific data analytics methodology for classifying and analyzing the swallowing events. Only one prototype of this class of wearables was developed by [PERSON] et al. [65]. The neckwear device contains microphones, a flex sensor, and an RFID reader. The microphones and the flex sensor are to be employed for sensing throat movement and chewing sound associated with medication swallowing activity. Hence, the authors embedded an RFID reader as they aim for adding another element of medication adherence verification by monitoring pills equipped with ingestible biosensors when passing through the throat area. However, the study in its current version does not include any validation trials, thus making it difficult to make conclusions about the performance, social acceptance, and comfort of this approach. Given the promise of acoustic sensing in food monitoring, it is highly likely that this technology will face the same challenges associated with other neck-worn sensors when applied in promoting medical compliance in older users [113]. * _Wrist-Worn Sensors_: When reviewing sensor-based systems, one should not ignore personal sensors. Personal sensors are a class of wearables that can be used for fashion and tracking purposes, such as smartwatches [114]. Nonetheless, these wearables embed miniaturized and continuously progressing capabilities including Inertial Measurements Units (IMUs) (accelerometer, gyroscope, and magnetometer or a combination of these) [115; 116]. Thus, wearable and personal sensors have been recently used in many healthcare monitoring studies, including medication intake detection.