A castable ball talks to a phone and fishes from a bank. A mounted unit has its own screen and needs a hull. Decide which before comparing prices.
Two machines, one word
A castable sonar is a ball on the end of a line that talks to a phone: the corpus prices them from about 99 € to 429 €, and they fish from a bank or a kayak with no boat at all.
A mounted unit has its own screen and a transducer on the hull: from about 167 € to 385 € here. It needs a boat, a battery and a bracket, and no listing sells all three together.
One listing is a third object entirely — a bait boat with sonar aboard at 289 €.
The three figures that matter
Depth range, printed on the cheaper units and decisive: 45 m is a lake unit.
Chirp, which means the unit sweeps a band rather than one frequency — the difference between two fish shown as one and two fish shown as two.
And GPS, which is what turns a reading into a place you can find again. It is the single feature that changes how the tool is used rather than how well it works.
Where this page disagrees with the maker’s own documentation, the documentation wins. Every length, casting weight, test curve, line diameter, breaking strain, reel size, retrieve per turn, drag force, buoyancy rating, mesh size and mass on this page is the maker’s own published figure, in the unit as printed, credited to whoever printed it. Nothing here is measured, and no figure is restated in another convention — a pound test curve is not turned into grams, and a kilogram of breaking strain is not turned into pounds, because a converted number is a different number. And the two ranges this page never adds together: a wireless range is measured through air, a depth through water. A sonar that reaches sixty metres from the phone and reads forty-five metres down has published two figures about two different media, and neither limits the other. This page prints each as the maker stated it, names which is which, and says so where a listing gives only one.
Any price inside this text was read on 22 September 2026; the live one sits at the top of the page.
The questions that keep coming back
What does Chirp mean?
That the unit sweeps a band of frequencies rather than pinging one note, which separates two fish that a single frequency shows as one. The corpus prints it on several Garmin and Deeper models.
Is GPS worth the difference?
It turns a depth reading into a map you can return to. The corpus prices the same castable unit at about 154 € without GPS and 193 € with it.
What does depth range tell me?
Whether the unit suits your water at all. One cheap unit in the corpus states 45 m, which is useless for Norwegian cod and ample for a French lake.
Last reviewed 22 September 2026