By Steve F., March 12, 2026

Elevator emergency phones are still fundamentally voice communication devices, making them one of the simplest POTS replacement scenarios. However, even in this seemingly straightforward application, significant challenges can arise if the technical and regulatory requirements of the industry are not fully understood.

1. The ASME A17.1/CSA B44 safety code for elevators

The ASME A17.1/CSA B44 safety code for elevators requires that emergency communication systems remain functional even during power failures or internet outages. As analog phone lines are phased out, modern, code-compliant systems (often VoIP or cellular) must have dedicated backup power and, in some cases, enhanced monitoring to ensure connectivity.

Key Requirements Regarding Communication Failure (2019/2022 Codes)

• Standby Power for Communication: If the primary power for the communication device fails, the system must automatically transfer to a standby/emergency power source capable of providing at least 4 hours of service.
• Phone Line Monitoring (PLM): The code requires that the operability of the phone line (or equivalent means, such as VoIP/cellular) is verified. If the connection fails, an alarm must be generated.
• Enhanced Monitoring (2019+): The 2019 code requires two-way, live video and text-based communication in addition to voice. This ensures passengers with speech or hearing impairments can communicate even if voice lines are degraded, and it helps verify the situation to reduce false calls.
• Alternative Communication: For elevators with over 60 feet of travel, code requires specialized on-site, in-building, or remote monitoring capabilities.
• Cybersecurity (2022 Update): As digital/internet connectivity increases, the 2022 code added specific cybersecurity requirements for remote monitoring and operation to protect against system tampering.
• Impact on Internet/Digital Failures Because these systems often use VoIP or cellular, a failure in the building's internet, a disconnected ethernet cable, or a localized cellular outage could affect the phone line. Therefore, modern systems often use a hybrid approach—such as a cellular-based backup—to ensure compliance with the "always-available" mandate of the A17.1/B44 code.

The Vola PR series fully complies with the requirements of the ASME A17.1/CSA B44 safety codes. These devices support 24 hours of standby time and 8 hours of talk time, significantly exceeding the minimum code requirements.

PR12 & PR08-Pro & PR18

Additionally, Vola PR series devices support dual internet connectivity, including:

• WAN (Ethernet)
• Cellular connectivity

Cellular connections support dual SIM cards and eSIM, enabling access to multiple wireless carriers and improving network reliability.

2. Line Voltage and Ring Signal Compatibility

Traditional PSTN networks provide a 48 VDC line feed voltage and a 90 Vrms / 20 Hz sinusoidal ringing signal. Many ATA devices designed for general VoIP applications cannot meet these electrical specifications. Typical consumer-grade ATA devices only support approximately 28 VDC line voltage and 40 Vrms ringing signals.

While this may work for most household telephones, it often causes problems with elevator emergency phones, particularly older models. Common issues include:

• Failure to detect off-hook status
• Ring signal incompatibility

The Vola PR series fully supports 48 VDC line voltage and 90 Vrms / 20 Hz ringing signals, ensuring compatibility with virtually all elevator emergency phones that previously operated on PSTN networks—even very old models.

3. CPC (Calling Party Control)

Most elevator phones operate in hands-free mode, and proper call termination relies on CPC (Calling Party Control) signals.

Although many ATA devices claim CPC support, the configuration of the CPC timer is critical. If the timing is too short or too long, elevator phones may fail to detect the signal or may behave unpredictably. Another important consideration is failure recovery. If the ATA sends a CPC signal but the call is not successfully terminated, the system must be able to detect the fault and restore normal operation. Many general-purpose ATA devices do not adequately address these edge cases.

The Vola PR series has been extensively tested with various elevator phone models. The default configuration works reliably with most devices without requiring additional tuning. Furthermore, all parameters can be remotely configured through the VolaCloud, allowing engineers to quickly diagnose and resolve compatibility issues if necessary.

VolaCloud

4. The P100 Protocol

P100 is a DTMF-based communication protocol similar to the Contact ID protocol used in alarm systems. It is commonly used by elevator phones to report system status, faults, or routine check-in messages to a monitoring center.

Typical P100 messages include:

Because P100 relies on DTMF signaling, it has strict requirements for tone duration and interval timing. In traditional PSTN networks, which provide synchronized timing across the entire network, this requirement is easily satisfied. However, in VoIP networks, latency, packet loss, and jitter can introduce compatibility issues.

When using VoLTE, the situation can become even more complex. Voice transcoding and the conversion of signaling into RFC2833 / RFC4733 events within the LTE core network may cause loss of critical DTMF timing information, leading to significant compatibility problems if not properly handled.

The Vola PR series includes specialized optimizations for both VoIP and VoLTE transmission, ensuring reliable operation of the P100 protocol.

5. Programming Elevator Phones

Many elevator phones support remote programming using DTMF commands. The DTMF transmission challenges discussed in the P100 section also apply to programming operations. The Vola PR series is designed to ensure reliable DTMF transmission for remote configuration.

However, elevator phone programming introduces additional security considerations. For security reasons, most elevator phones do not allow programming simply by calling the device directly.

Because elevator phones operate in hands-free mode, allowing unrestricted incoming calls could enable unauthorized individuals to listen to conversations inside the elevator cabin. Therefore, programming must follow a specific secure procedure rather than simple inbound dialing.

6. VoLTE or VoIP?

As analog phone lines are phased out, elevator communication systems using cellular connectivity typically choose between VoIP over LTE and Native VoLTE.

VoIP provides advantages such as:

• Centralized number management by the MSP
• Better compatibility with DTMF-based protocols like P100
• Easier support for remote device programming

VoLTE, on the other hand, benefits from higher network priority within LTE infrastructure, which may provide better performance during network congestion.

However, VoLTE has limitations, including:

• Poor compatibility with DTMF-based signaling protocols
• Phone numbers are controlled by the mobile carrier rather than the MSP

The Vola PR series has been optimized to support both VoIP and VoLTE environments, ensuring reliable voice communication, P100 signaling, and device programming.

Through collaboration with Tango Networks, Vola also provides a hybrid VoLTE + VoIP solution. This architecture allows elevator calls to benefit from VoLTE’s network priority while enabling MSPs to manage phone numbers through their own UC platforms.

Customers interested in this solution are encouraged to contact a Vola sales representative for further details.

7. High Availability and Remote Fault Monitoring

Unlike standard desktop phones, elevator emergency phones are life-safety critical systems.

Most ATA devices designed for office telephony are not high-availability systems and are therefore unsuitable for life-safety applications. The Vola PR series has been specifically engineered for high availability at both the hardware and software levels. With integrated battery backup and industrial-grade design, these devices provide a reliable platform for POTS replacement deployments.

Through the VolaCloud management platform, MSPs can receive real-time alerts via email or SMS whenever faults occur on telephone lines connected through Vola PR devices. This capability helps MSPs more easily meet the monitoring and reliability requirements defined in the ASME A17.1 safety code.