# Non-Contact and Non-Intrusive Add-on IoT Device for Wireless Remote Elevator Control
## 6 Discussion and Conclusions
The label APXC means that there is an AP in the Corridor (C) of the plant X, some meters away from the elevator, while the label APXL means that there is an AP in the lobby (L) of the elevator of the plant X. An inspection of the building infrastructure revealed that all the plants were designed to have one AP in the elevator lobby and another in the nearby corridor. However, in practice, there are only two floors with an AP in the elevator lobby area (AP2L and AP0L), three floors with an AP in the corridor (AP3C, AP2C and AP1C) and one floor without any nearby AP. This asymmetric distribution (see Figure 18) was the cause of the wireless network problems experienced depending on the floor where the smartphone and the elevator were. In practice, these non-critical wireless communication problems observed during the experimentation with the IoT device for elevator control be avoided simply by revising the distribution of the access points in the building. The possibility of using a QR code to automatically call the elevator and open its web interface was evaluated. In the case of this application, the white background of the QR code contrasts with the dark color of the walls and doors of the elevator, and the QR code was detected successfully from different distances. The results show that a relatively small QR code (\(7\times 7\) cm, Figure 15) can be read with a 100% success from a distance ranging from 0.22 m to 2.5 m, so there is no need to get closer to the elevator to use the QR code feature. In a last experiment, the machine-to-machine communication performance of the IoT device was evaluated with a mobile robot calling the elevator using TCP to send the control orders. In this case, the elevator was successfully accessed in 100% of the calls, probably because of the superior performance of the wireless antenna of the mobile robot and the automatic management of network communication errors performed by a TCP communication. As a summary, the advantages of the IoT device proposed for elevator control are: (i) its relative low cost, because it is based on standard electronic devices and servomotors; (ii) its non-contact remote control performances; and (iii) its non-intrusive application in virtually any kind of elevator. These performances allow the device to be used as a rapid response tool in order to increase the non-contact accessibility to elevators. Conversely, the main drawback of the current implementation of the IoT device was its power consumption, which required the use of a large battery to ensure a weekly operation. In general, the strategy used to reduce the current on IoT devices is to make them enter sleep mode when not accessed and wake up when receiving a message. The disadvantage of this strategy is that it greatly increases the latency (response time) of the device, so it was discarded because the device had no size or battery limitation. Finally, the non-contact add-on wireless IoT device proposed in this paper for remote elevator control has indirectly addressed the challenges identified by [PERSON] et al. [39], as it avoids the need to locate and identify the elevator button panel and the challenges of interacting with its buttons.