Eazlock — IoT Device Locking & EMI Management

Overview

Eazlock (https://eazlock.com) is an IoT device management and installment (EMI) financing platform built for Yupsis. It helps consumer electronics distributors and smartphone retailers manage financed devices safely.

If a customer misses an installment payment deadline, Eazlock automatically coordinates staged restrictions—such as on-screen payment reminders, sound alerts, outgoing call restrictions, or lock screens—and instantly restores normal device access the moment an online payment is confirmed through digital wallets or bank rails.

Architecture & How It Works

Communicating with mobile devices across unstable cellular networks requires careful queue design:

• Asynchronous Command Buffering: We never assume a target phone is online right now. If a device is powered off, in airplane mode, or out of cellular coverage, commands wait safely in a stateful pending queue in Redis/PostgreSQL until the device reconnects.
• Sequence Numbers & Idempotency: Every command has a sequential version number. This prevents race conditions where an older "lock" command delayed by network latency arrives after a newer "unlock" command.
• Automated Midnight Schedulers: Cron workers run every midnight to check payment deadlines, advance accounts through grace periods, and dispatch reminders before initiating any device restrictions.
• Signed Hardware Payloads: Commands are cryptographically signed to ensure only authorized server instructions can alter the device state.

Practical Engineering Challenges & Solutions

1. Handling Disconnected and Offline Devices

• Problem: Borrowers facing payment deadlines frequently turn off their phones or disconnect from mobile data. Standard HTTP push requests immediately fail with connection timeouts.
• Solution:
  • Built a DevicePendingCommandProcessor queue.
  • When a command is triggered, it persists with a PENDING state.
  • The enrolled device application periodically sends a lightweight heartbeat ping.
  • As soon as the heartbeat arrives, the server delivers pending commands in exact order and waits for cryptographic execution receipts.

2. Preventing Conflicting Command Replays

• Problem: If a customer pays their installment at 10:00 AM, the system sends an "UNLOCK" command. If a delayed "LOCK" command from the night before was still in transit over slow 2G data, executing it out of order could lock the phone right after the customer paid.
• Solution:
  • Assigned monotonically increasing sequence numbers and timestamps to every device state transition.
  • The device client drops any incoming command that carries a sequence number lower than or equal to its current state, ensuring only the latest instructions take effect.

3. Gradual Enforcement Without Abrupt Disruption

• Problem: Immediately locking a customer's phone on day one of a missed payment harms customer trust and increases support ticket volume.
• Solution:
  • Designed a flexible grace-period matrix:
    • Day 1–3: Gentle on-screen payment reminders and daily SMS alerts.
    • Day 4–6: Audible notification chimes and payment prompts during device wake.
    • Day 7+: Restrict outgoing non-emergency actions until payment confirmation.
  • Once the digital payment gateway confirms the installment, the system immediately dispatches the unlock instruction without manual staff intervention.

Tech Stack

Key Results

• Zero Dropped Instructions: Offline devices receive and execute pending commands safely the moment they reconnect.
• Automated Payment Lifecycle: Staged reminders and instant automatic unlocks reduce customer disputes and administrative workload.
• Reliable Device Fleet Management: Distributors monitor thousands of enrolled devices securely from a single dashboard.