How to Monitor Ethereum Address Balance Changes: 3 Effective Methods

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Monitoring changes in Ethereum address balances—whether for ETH or ERC-20 tokens—is a fundamental requirement in blockchain application development. Whether you're building a wallet, exchange, DeFi platform, or analytics tool, staying updated with balance movements ensures your system reacts accurately and in real time.

This article explores three proven methods to monitor Ethereum address balances: periodic polling, listening to smart contract events, and block scanning. Each approach has unique advantages, trade-offs, and ideal use cases. We’ll break down implementation steps, provide practical code examples using ethers.js v6, and help you choose the best strategy based on performance, accuracy, and resource constraints.

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Method 1: Periodic Polling

Periodic polling is the most straightforward way to monitor an Ethereum address’s balance. It involves repeatedly querying the blockchain at fixed intervals to check for updates.

Implementation Steps

  1. Set up a timer to trigger balance checks at regular intervals (e.g., every 10 seconds).
  2. Use a provider like ethers.JsonRpcProvider to fetch the current balance.
  3. Compare the new value with the previously recorded one.
  4. Trigger actions if a change is detected.

Pros and Cons

Advantages:

Disadvantages:

Code Example Using ethers.js (v6)

const { ethers } = require('ethers');

const provider = new ethers.JsonRpcProvider('your_rpc_url');
let lastBalance = BigInt(0);

async function checkBalance(address) {
  try {
    const currentBalance = await provider.getBalance(address);
    if (currentBalance !== lastBalance) {
      console.log(`Balance changed: ${ethers.formatEther(currentBalance)} ETH`);
      lastBalance = currentBalance;
    }
  } catch (error) {
    console.error('Error fetching balance:', error);
  }
}

// Check every 30 seconds
setInterval(() => checkBalance('0xYourEthereumAddress'), 30000);

You can also use public APIs like Etherscan:

const axios = require('axios');
const API_KEY = 'your_api_key';

async function getBalanceFromEtherscan(address) {
  const url = `https://api.etherscan.io/api?module=account&action=balance&address=${address}&tag=latest&apikey=${API_KEY}`;
  const response = await axios.get(url);
  const balanceInWei = BigInt(response.data.result);
  console.log(`Balance: ${ethers.formatEther(balanceInWei)} ETH`);
}

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Method 2: Listening to Smart Contract Events

For ERC-20 or other token balances, listening to Transfer events emitted by smart contracts offers a more efficient alternative.

Understanding Ethereum Events

Smart contracts emit events when specific actions occur—such as transferring tokens. These logs are stored on-chain and can be subscribed to in real time via WebSocket providers.

This method is ideal for tracking token transfers involving your address.

Implementation Steps

  1. Identify the relevant event (usually Transfer with indexed from and to fields).
  2. Connect to a WebSocket-enabled provider.
  3. Subscribe to the event filter targeting your address.
  4. Parse incoming event data to determine balance impact.

Pros and Cons

Advantages:

Disadvantages:

Code Example: Monitoring ERC-20 Transfers

const { ethers } = require('ethers');

const provider = new ethers.WebSocketProvider('wss://ethereum-rpc.example.com');
const contractAddress = '0xTokenContractAddress';
const abi = [
  'event Transfer(address indexed from, address indexed to, uint256 value)'
];

const contract = new ethers.Contract(contractAddress, abi, provider);

// Filter for transfers to or from our address
const userAddress = '0xYourWalletAddress';

contract.on('Transfer', (from, to, value) => {
  if (from === userAddress || to === userAddress) {
    const direction = from === userAddress ? 'Outgoing' : 'Incoming';
    console.log(`${direction} transfer of ${ethers.formatUnits(value, 18)} tokens`);
    console.log(`Transaction hash: ${event.log.transactionHash}`);
  }
});

Method 3: Block Scanning (Block Parsing)

Block scanning provides the most comprehensive monitoring by analyzing every transaction in each new block.

How It Works

Instead of relying on events or periodic queries, this method:

It's often used in blockchain explorers and custodial systems requiring full auditability.

Implementation Steps

  1. Connect to an Ethereum node via JSON-RPC or WebSocket.
  2. Track the latest block number.
  3. On each new block, retrieve its full transaction list.
  4. Inspect from and to fields for matches.
  5. Reconstruct balance changes based on transaction flow.

Pros and Cons

Advantages:

Disadvantages:

Code Example: Real-Time Block Scanner

const { ethers } = require('ethers');
const ADDRESS_TO_MONITOR = '0xYourAddress';

const provider = new ethers.JsonRpcProvider('your_rpc_url');
let lastBlockNumber;

async function startBlockScanner() {
  lastBlockNumber = await provider.getBlockNumber();

  console.log(`Starting scanner from block ${lastBlockNumber}`);

  provider.on('block', async (blockNumber) => {
    if (blockNumber > lastBlockNumber + 10) {
      // Handle potential missed blocks
      console.warn('Missed some blocks, consider backfilling');
    }

    const block = await provider.getBlock(blockNumber, true);
    block.prefetchedTransactions.forEach((tx) => {
      if (tx.from === ADDRESS_TO_MONITOR || tx.to === ADDRESS_TO_MONITOR) {
        console.log(`Detected transaction: ${tx.hash}`);
      }
    });

    lastBlockNumber = blockNumber;
  });
}

startBlockScanner();

Frequently Asked Questions (FAQ)

Q: Can I monitor native ETH transfers using smart contract events?
A: No. Native ETH transfers do not emit smart contract events. You must rely on polling or block scanning to detect them.

Q: Which method is best for real-time alerts?
A: Listening to contract events offers the lowest latency for token transfers. For ETH, combine event listening with frequent polling or block scanning.

Q: Is there a risk of missing data with event listeners?
A: Yes. If your service goes offline, you may miss events. To prevent this, store the last processed block and replay logs after reconnecting.

Q: How do I reduce API costs when polling frequently?
A: Use caching, increase interval times for low-priority addresses, or switch to a WebSocket-based solution with event filtering.

Q: Can I monitor multiple addresses efficiently?
A: Polling becomes inefficient at scale. For large-scale monitoring, consider dedicated indexing services or building a custom indexer using The Graph or Alchemy Notify.

Q: Are there tools that simplify balance monitoring?
A: Yes—platforms like Alchemy, Infura, and Moralis offer webhook-based notifications. Alternatively, self-hosted solutions using ethers.js give more control.

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Conclusion

Choosing the right method to monitor Ethereum address balances depends on your application's needs:

In production environments, many applications combine these methods—using event listeners for speed and block scanning for reconciliation.

By understanding the strengths and limitations of each approach, developers can build robust, responsive, and reliable blockchain applications that react instantly to financial activity.

Whether you're securing user funds or powering real-time dashboards, effective balance monitoring is the foundation of trustless systems on Ethereum.