diff --git a/ethcore/src/client/chain_notify.rs b/ethcore/src/client/chain_notify.rs
index 897c8cfac..737cd0153 100644
--- a/ethcore/src/client/chain_notify.rs
+++ b/ethcore/src/client/chain_notify.rs
@@ -20,7 +20,8 @@ use util::H256;
 /// Represents what has to be handled by actor listening to chain events
 #[derive(Ipc)]
 pub trait ChainNotify : Send + Sync {
-	/// fires when chain has new blocks
+	/// fires when chain has new blocks, not including those encountered during
+	/// a major sync.
 	fn new_blocks(&self,
 		_imported: Vec<H256>,
 		_invalid: Vec<H256>,
diff --git a/ethcore/src/snapshot/mod.rs b/ethcore/src/snapshot/mod.rs
index 89e4ed8ba..979089331 100644
--- a/ethcore/src/snapshot/mod.rs
+++ b/ethcore/src/snapshot/mod.rs
@@ -45,6 +45,7 @@ use rand::{Rng, OsRng};
 
 pub use self::error::Error;
 pub use self::service::{RestorationStatus, Service, SnapshotService};
+pub use self::watcher::Watcher;
 
 pub mod io;
 pub mod service;
@@ -52,6 +53,7 @@ pub mod service;
 mod account;
 mod block;
 mod error;
+mod watcher;
 
 #[cfg(test)]
 mod tests;
diff --git a/ethcore/src/snapshot/watcher.rs b/ethcore/src/snapshot/watcher.rs
new file mode 100644
index 000000000..d2dd1d7dc
--- /dev/null
+++ b/ethcore/src/snapshot/watcher.rs
@@ -0,0 +1,177 @@
+// Copyright 2015, 2016 Ethcore (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Watcher for snapshot-related chain events.
+
+use client::{BlockChainClient, Client, ChainNotify};
+use ids::BlockID;
+use service::ClientIoMessage;
+use views::HeaderView;
+
+use io::IoChannel;
+use util::hash::H256;
+
+use std::sync::Arc;
+
+// helper trait for transforming hashes to numbers.
+trait HashToNumber: Send + Sync {
+	fn to_number(&self, hash: H256) -> Option<u64>;
+}
+
+impl HashToNumber for Client {
+	fn to_number(&self, hash: H256) -> Option<u64> {
+		self.block_header(BlockID::Hash(hash)).map(|h| HeaderView::new(&h).number())
+	}
+}
+
+/// A `ChainNotify` implementation which will trigger a snapshot event
+/// at certain block numbers.
+pub struct Watcher {
+	oracle: Arc<HashToNumber>,
+	channel: IoChannel<ClientIoMessage>,
+	period: u64,
+	history: u64,
+}
+
+impl Watcher {
+	/// Create a new `Watcher` which will trigger a snapshot event
+	/// once every `period` blocks, but only after that block is
+	/// `history` blocks old.
+	pub fn new(client: Arc<Client>, channel: IoChannel<ClientIoMessage>, period: u64, history: u64) -> Self {
+		Watcher {
+			oracle: client,
+			channel: channel,
+			period: period,
+			history: history,
+		}
+	}
+}
+
+impl ChainNotify for Watcher {
+	fn new_blocks(
+		&self,
+		imported: Vec<H256>,
+		_: Vec<H256>,
+		_: Vec<H256>,
+		_: Vec<H256>,
+		_: Vec<H256>,
+		_duration: u64)
+	{
+
+		let highest = imported.into_iter()
+			.filter_map(|h| self.oracle.to_number(h))
+			.filter(|&num| num >= self.period + self.history)
+			.map(|num| num - self.history)
+			.filter(|num| num % self.period == 0)
+			.fold(0, ::std::cmp::max);
+
+		if highest != 0 {
+			if let Err(e) = self.channel.send(ClientIoMessage::TakeSnapshot(highest)) {
+				warn!("Snapshot watcher disconnected from IoService: {}", e);
+			}
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::{HashToNumber, Watcher};
+
+	use client::ChainNotify;
+	use service::ClientIoMessage;
+
+	use util::{H256, U256, Mutex};
+	use io::{IoContext, IoHandler, IoService};
+
+	use std::collections::HashMap;
+	use std::sync::Arc;
+
+	struct TestOracle(HashMap<H256, u64>);
+
+	impl HashToNumber for TestOracle {
+		fn to_number(&self, hash: H256) -> Option<u64> {
+			self.0.get(&hash).cloned()
+		}
+	}
+
+	struct Handler(Arc<Mutex<Vec<u64>>>);
+
+	impl IoHandler<ClientIoMessage> for Handler {
+		fn message(&self, _context: &IoContext<ClientIoMessage>, message: &ClientIoMessage) {
+			match *message {
+				ClientIoMessage::TakeSnapshot(num) => self.0.lock().push(num),
+				_ => {}
+			}
+		}
+	}
+
+	// helper harness for tests.
+	fn harness(numbers: Vec<u64>, period: u64, history: u64) -> Vec<u64> {
+		let events = Arc::new(Mutex::new(Vec::new()));
+
+		let service = IoService::start().unwrap();
+		service.register_handler(Arc::new(Handler(events.clone()))).unwrap();
+
+		let hashes: Vec<_> = numbers.clone().into_iter().map(|x| H256::from(U256::from(x))).collect();
+		let mut map = hashes.clone().into_iter().zip(numbers).collect();
+
+		let watcher = Watcher {
+			oracle: Arc::new(TestOracle(map)),
+			channel: service.channel(),
+			period: period,
+			history: history,
+		};
+
+		watcher.new_blocks(
+			hashes,
+			vec![],
+			vec![],
+			vec![],
+			vec![],
+			0,
+		);
+
+		drop(service);
+
+		// binding necessary for compilation.
+		let v = events.lock().clone();
+		v
+	}
+
+	#[test]
+	fn should_not_fire() {
+		let events = harness(vec![0], 5, 0);
+		assert_eq!(events, vec![]);
+	}
+
+	#[test]
+	fn fires_once_for_two() {
+		let events = harness(vec![14, 15], 10, 5);
+		assert_eq!(events, vec![10]);
+	}
+
+	#[test]
+	fn finds_highest() {
+		let events = harness(vec![15, 25], 10, 5);
+		assert_eq!(events, vec![20]);
+	}
+
+	#[test]
+	fn doesnt_fire_before_history() {
+		let events = harness(vec![10, 11], 10, 5);
+		assert_eq!(events, vec![]);
+	}
+}
\ No newline at end of file